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Register now and save up to $200 Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Most awarded test prep in the world Now free for 30 days Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code ## Salt Water Pools tagged by: This topic has 5 expert replies and 12 member replies Goto page • 1, • 2 ### GMAT/MBA Expert David@VeritasPrep GMAT Instructor Joined 22 Feb 2010 Posted: 2193 messages Followed by: 508 members Upvotes: 1186 GMAT Score: 770 #### Salt Water Pools Sat Aug 28, 2010 9:28 am Okay, by request, here we go with a bold-faced reasoning question. The latest adaptation in swimming pools is the “saltwater” pool. The water in such pools is 1/10 as salty as the ocean. The salt content is about that of the human body. Owners of such pools claim that there is no irritation from chlorine and that the salt water actually soothes and softens the skin. They also claim that such pools are less expensive to maintain than traditional freshwater pools. However, manufacturers of pool chemicals, such as chlorine, claim that the salt water system is more expensive to install and can leave behind a salt residue on some surfaces. A) The first portion lists two potential advantages of implementing a new system; The second portion lists an unrelated pair of possible disadvantages to implementing the system. B) The first portion is an unproven claim regarding a new system, the second portion is evidence supporting this claim. C) The first portion is the main conclusion of the argument; The second portion is an unintended consequence of the main conclusion. D) The first portion lists two possible advantages of implementing a new system; The second portion directly refutes those advantages. E) The first portion is an unproven claim regarding a new system; the second portion is a prediction of potential consequences. _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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### GMAT/MBA Expert

David@VeritasPrep GMAT Instructor
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Wed Jan 05, 2011 12:17 pm
mundasingh -

When I first read what you wrote I was a little worried because it is true that claims made by those in favor and opposed to the salt water pools might not actually be advantages or disadvantages, they might just be the kind of claims made by American political candidates - basically lies.

However, in this case you will see that the correct answer - A- says "potential advantages" and "possible disadvantages" I think that this gives enough room for the claims to turn out not to be true. That is why they are just "potential" and "possible."

What do you think?

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Save $100 off any live Veritas Prep GMAT Course Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now! mundasingh123 Legendary Member Joined 15 Jan 2010 Posted: 2330 messages Followed by: 26 members Upvotes: 56 Wed Jan 05, 2011 2:05 am Hi David, In A, we are talking about advantages and when we say advantages arent we refrring to facts where as the statement are actually claims. Less Chlorine and softer skin are claims made by the owners.is it correct to bracket them under advantages. Similar High Installation Cost and Salt Residue are claims made by the Suppliers of Chlorine. gmatmachoman Legendary Member Joined 28 Jul 2008 Posted: 2326 messages Followed by: 2 members Upvotes: 173 Target GMAT Score: 740 GMAT Score: 710 Sat Aug 28, 2010 9:46 am I am over A vs E. but i feel A brings in more clarity of the 2 bold faced portions. niksworth Legendary Member Joined 14 Jun 2010 Posted: 520 messages Followed by: 6 members Upvotes: 70 Sat Aug 28, 2010 9:47 am A should be correct. The two boldfaces sentences are two claims which run parallel to each other but on separate tracks and in opposite directions! B - While the first portion may or may not be an unproven claim, the second portion is not an evidence supporting it. On the contrary, it is a counterclaim intended to nullify the advantages of the first claim. C - First portion is hardly a conclusion of the argument. In fact, it is a premise. The second portion is not a consequence of any conclusion. In fact this argument does not have a conclusion. It is a set of premises. D - While the first portion lists advantages of the new system, the second portion does not directly refute those advantages. Rather it states two disadvantages unrelated to the first two advantages. E - We do not know whether the first claim is unproven or not, but the second portion is not a prediction of potential consequences. It runs parallel to the first claim but in opposite direction. FightWithGMAT Master | Next Rank: 500 Posts Joined 20 Apr 2010 Posted: 364 messages Followed by: 3 members Upvotes: 31 Target GMAT Score: 700 Sat Aug 28, 2010 10:52 am David@VeritasPrep wrote: Okay, by request, here we go with a bold-faced reasoning question. The latest adaptation in swimming pools is the “saltwater” pool. The water in such pools is 1/10 as salty as the ocean. The salt content is about that of the human body. Owners of such pools claim that there is no irritation from chlorine and that the salt water actually soothes and softens the skin. They also claim that such pools are less expensive to maintain than traditional freshwater pools. However, manufacturers of pool chemicals, such as chlorine, claim that the salt water system is more expensive to install and can leave behind a salt residue on some surfaces. A) The first portion lists two potential advantages of implementing a new system; The second portion lists an unrelated pair of possible disadvantages to implementing the system. B) The first portion is an unproven claim regarding a new system, the second portion is evidence supporting this claim. C) The first portion is the main conclusion of the argument; The second portion is an unintended consequence of the main conclusion. D) The first portion lists two possible advantages of implementing a new system; The second portion directly refutes those advantages. E) The first portion is an unproven claim regarding a new system; the second portion is a prediction of potential consequences. IMO E. I think Chlorine and Salt are 2 different contents of pools. Becoz from the chlorine manufacturer's statement we can find that he is not in favor of salt water. He would still favor Chlorine to Salt water. So first does seem to present 2 advantages. reply2spg Legendary Member Joined 14 Sep 2008 Posted: 1261 messages Upvotes: 27 Target GMAT Score: 801 GMAT Score: 570 Sat Aug 28, 2010 11:03 am I can never be right in bold faced questions. I don't know how to solve them? IMO D. _________________ Sudhanshu (have lot of things to learn from all of you) ### GMAT/MBA Expert David@VeritasPrep GMAT Instructor Joined 22 Feb 2010 Posted: 2193 messages Followed by: 508 members Upvotes: 1186 GMAT Score: 770 Sat Aug 28, 2010 3:21 pm OA is A Nice analysis "Niksworth." The correct answer will describe the roles of both portions in bold. The first portion describes two possible advantages of the new salt water system. The second portion replies with two disadvantages that are not directly related to the two advantages listed in the first statement. These advantages and disadvantages may seem to be related, but the two advantages are “no chlorine irritation” and “softer skin,” while the two disadvantages are “costs more to install” and “can leave behind a residue on surfaces.” These are not directly related. The non-bold portion in between does mention cost savings and would be related to the disadvantages, but this portion is not bold-faced. Choice A correctly describes the roles of each of these statements and is the best answer. Choice D is very close to this, but incorrectly describes the second portion as directly refuting the advantages stated in the first. Choice B, C, and E each describe both portions incorrectly. The first portion is not evidence for a claim, it is a claim. The first portion is also not the main conclusion, but merely some possible advantages. “reply2spg” - the way that I like to approach these questions is to work with one bold-faced portion first. I start with whichever portion I understand the best and I go through all of the answer choices looking at that portion. When I have eliminated all of the possible choices there I am left with two or three choices. I then use the other bold-faced portion to eliminate remaining choices and make the final decision. In this case, if I recognized that the first portion contained some claim advantages, and was not the main conclusion, (eliminate choice C) and was not evidence for a claim but is actually a claim (eliminate E). A, B, and D can then be evaluated using the second bold faced portion. B can be eliminated because the second portion does not support the first. Then we go to A and D and the question comes down to whether the disadvantages are directly related to the advantages as discussed above. By the way, if you enjoy these and want more questions and more useful advice on approaching difficult types of questions like assumptions, "most useful to know," plan questions, and” best completes the passage,” then you should check out the Veritas Critical Reasoning 2 book - I happen to have written many of the questions in that book! Thanks! _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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ankurmit Legendary Member
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Mon Aug 30, 2010 10:50 pm
IMO A

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Ankur mittal

norizam Junior | Next Rank: 30 Posts
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David@VeritasPrep wrote:
Okay, by request, here we go with a bold-faced reasoning question.

The latest adaptation in swimming pools is the “saltwater” pool. The water in such pools is 1/10 as salty as the ocean. The salt content is about that of the human body. Owners of such pools claim that there is no irritation from chlorine and that the salt water actually soothes and softens the skin. They also claim that such pools are less expensive to maintain than traditional freshwater pools. However, manufacturers of pool chemicals, such as chlorine, claim that the salt water system is more expensive to install and can leave behind a salt residue on some surfaces.

A) The first portion lists two potential advantages of implementing a new system; The second portion lists an unrelated pair of possible disadvantages to implementing the system.

B) The first portion is an unproven claim regarding a new system, the second portion is evidence supporting this claim.

C) The first portion is the main conclusion of the argument; The second portion is an unintended consequence of the main conclusion.

D) The first portion lists two possible advantages of implementing a new system; The second portion directly refutes those advantages.

E) The first portion is an unproven claim regarding a new system; the second portion is a prediction of potential consequences.
Here's what I thought:
The first portion is a claim ( so C is out) and the second is countering the claim (by the use of "however", so B and D are out -D does not directly refute the first portion). So only A and E are left.
I chose A because the bold parts seem to play good parts/bad parts rather than actions/consequences

Target2009 Legendary Member
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Tue Jan 04, 2011 9:10 pm
IMO - A

manojks Junior | Next Rank: 30 Posts
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Mon Feb 21, 2011 9:04 am
My pick "A"
Is it right?

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Mon Feb 21, 2011 10:44 am
Yes! You are right... Official Answer is A.

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Save $100 off any live Veritas Prep GMAT Course Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now! nikhilsrl Master | Next Rank: 500 Posts Joined 10 Jan 2011 Posted: 109 messages Followed by: 7 members Upvotes: 8 Test Date: 26/Mar/2011 GMAT Score: 760 Mon Feb 28, 2011 1:43 am Hello David, As per E - the first portion refers to an unproven claim. Aren't owners making an unproven claim. Again as per E - the second portion is a prediction of potential consequences. Aren't the manufacturers predicting the potential consequences. As for A - The first portion lists two potential advantages of implementing a new system. Now what are two advantages. I see only one - "the salt water actually soothes and softens the skin". "there is no irritation from chlorine" cannot really be an advantage, it just negates any disadvantage of chlorine. Please clarify. ### GMAT/MBA Expert David@VeritasPrep GMAT Instructor Joined 22 Feb 2010 Posted: 2193 messages Followed by: 508 members Upvotes: 1186 GMAT Score: 770 Mon Feb 28, 2011 6:22 am Certainly that is an advantage! The absence of a disadvantage (in this case pain) is an advantage. In fact, I would dare say that a large percentage of "advantages" out there in the world are in fact the absence of disadvantages. Does your toothpaste say it "prevents cavities"? This is not an advantage such as "giving you new teeth" would be - it is only the absence of a disadvantage - cavities. Likewise "low in saturated fat" "interest free financing" and so forth would not count as advantages by your definition. _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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text:
## vertical asymptotes

find all possible vertical asymptotes for f(x)= (x^2 -4)/(x^2 -2x-15) choosing one of your answer, show with a graphing table on your calculator that it actually is an assymptote.

format: plain


text:
# Solving Proportions

Have you ever played dominoes? In the standard set of dominoes,
7 out of 28 tiles, or one-fourth of the tiles, are doubles.

The ratios $$\frac{7}{28}$$ and $$\frac{1}{4}$$ are equivalent.
That is $$\frac{7}{28}$$ = $$\frac{1}{4}$$.
The equation $$\frac{7}{28}$$ = $$\frac{1}{4}$$ is an example of a proportion.

A proportion is an equation that shows that two ratios are equivalent.
One way to determine whether two ratios form a proportion is to find their If the cross products of two ratios are equal, then the ratios form a proportion. In the proportion shown, notice that the cross products, 6 x 3 and 9 x 2, are equal.
Use cross products to determine whether each pair of ratios forms a proportion. $$\frac{6}{15}$$ , $$\frac{4}{10}$$ ;
$$\frac{12}{20}$$ , $$\frac{9}{18}$$

If one value in a proportion is unknown, you can use cross products to solve the proportion.
Solve the proportion: $$\frac{12}{30}$$ = $$\frac{x}{10}$$

Explain, in your own words, the meaning of proportion.
Tell how you can determine whether two ratios form a proportion.
Use pattern blocks to build a proportion. Draw a picture of your model and explain why the two ratios are proportional.
Problems:

• If a room contains 42 people who are married and 30 people who are single, what is the ratio of married people to single people?
• Karina earned $32,000 last year and Tamara earned$42,000. What is the ratio of Karina’s earnings to Tamara’s?
• A runner ran 4.9 miles yesterday and 7.7 miles today. What is the ratio of the distance she ran yesterday to the distance she ran today?
• A political organization has a 7:1 ratio of members who are registered to vote to members who aren’t registered. If the organization has 28 registered members, how many nonregistered members does it have?
• A house has a 9:2 ratio of windows to doors. If it has four doors, how many windows does it have?
• Suppose that a store expects a 3 to 10 ratio of people who make a purchase to the number of people who enter the store. If 120 customers entered the store on a busy Saturday, how many made purchases?


text:
>When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Use a free body diagram (FBD) of the cut piece to solve for the unknown internal axial forces in the members that cross the cut. Why corner columns have higher values of moments than other columns? Method of section is very useful when you want to know the forces acting on a certain member in a truss. Method of joints We can determine the forces in all the members of the truss by using the method of joints. Let us consider the same diagram as before. The section must cut completely through the truss and should cut through no more than three members. Resources for Structural Engineers and Engineering Students. Classification of Bridges-Types, Span, Functions and Construction. THE METHOD OF JOINTS (Section 6.2) When using the method of joints to solve for the forces in truss members, the equilibrium of a joint (pin) is considered. The method of sections is often utilized when we want to know the forces in just a few members of a complex truss. The method centers on the joints or connection points between the members, and it is usually the fastest and easiest way to solve â¦ That is, you need to work from the sides towards the center of the truss. Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. www.spoonfeedme.com.au spoonfeedme.com.au more videos available at www.spoonfeedme.com.au P-424, determine the force in BF by the method of joints and then check this result using the method of sections. The primary benefit of the method of sections is that, for a determinate truss, you can find the force in any individual member quickly without having to solve through the entire truss one joint at a time (which you must do when using the method of joints). joints in a certain order. Then move to the next joint and find the forces in the members.Repeat the procedure and find all the member forces. This includes all external forces (including support reactions) as well as the forces acting in the members. Method of joints are the common method for the analysis of truss members.The basic concept that is used in the analysis is ,since the truss is in equilibrium the each joints in the truss is also in equilibrium, The steps for the determination of member forces, For the determination of reaction forces , we can use two equilibrium equations that is, Now we got two reactions,then choose a joint which has 2 unknown forces so as to find the two unknown forces from the two reaction we got, Take the joints and apply equations of equilibrium on that joint and find the member forces. Below is an example that is solved using both of these methods. So, we will start with section b-b to find $F_{AB}$ which we will then use in section a-a to find the forces in the other three members. It makes sense to choose this side because it does not have any external forces and it has only one reaction component $I_y$. For this problem, one way to do this is by cutting at section b-b as shown in FigureÂ 3.9. This is a simple truss that is simply supported (with pin at one end and a roller at the other). This section shares member AB with the other section a-a. For a simpler problem, only one cut would be needed if the section had only three members crossing the cut. Which one is the best for RCC concrete, M-sand or river sand? What is the biggest cost in the construction industry today? Trusses: Method of Sections Frame 19-1 *Introduction In the preceding unit you learned some general facts about trusses as well as a method of solution called the "Method of Joints." Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. For the truss shown in Fig. The sections are obtained by cutting through some of the members of the truss to expose the force inside the members. Method of Sections. Thus both the methods are used for the same purpose. The method involves breaking the truss down into individual sections and analyzing each section as a separate rigid body. This method permits us to solve directly any member by analyzing the left or the right section of the cutting plane. This section was chosen deliberately because the other three forces ($F_{BG}$, $F_{EG}$, and $F_{GH}$) all point direction through point G. So, if we evaluate the moment equilibrium about point G, we can solve directly for $F_{AB}$: which is negative, meaning that the member is actually in compression. For this problem, as previously described, we need to make two cuts and solve the equilibrium equations twice: once to find the force in member AB using section b-b and again to find the rest of the forces in the other members that cross section a-a. Joints and Sections Theory of Structure - I Lecture Outlines Method of Joints. the number of members is less than the required members.So there will be chance to fail the structure. There is also no internal instability, and therefore the truss is stable. They are used to span greater distances and to carry larger loads than can be done effectively by a single beam or â¦ All of the unknown member forces across the cut are shown, and are assumed to be in tension (pulling away from the member). As before, even though points A and F are not within the section cut, they are left in the diagram as reference points. The remaining unknowns may be found using vertical and horizontal equilibrium: The information on this website is provided without warantee or guarantee of the accuracy of the contents. In the Method of Joints, we are dealing with static equilibrium at a point. What will happen to a steel frame overloaded at bolt? The first diagram below is the presented problem for which we need to find the truss element forces. The author shall not be liable to any viewer of this site or any third party for any damages arising from the use of this site, whether direct or indirect. Since there are only three global equilibrium equations, we can only solve for three unknown member axial forces at a time using the method of sections. Step 1: Calculate the Reactions at the Supports. Truss: Method of. To do this, we need to find a way to cut the truss such that we include one of the unknown forces from a-a, but which is also cut in a way that we can directly solve for that unknown force. Newton's Third Law indicates that the â¦ Figure 1. View 04 Truss- Method of Joints and Sections.ppt from CIVIL ENGI 501 at U.E.T Taxila. That is, you need to work from the sides towards the center of the truss. Hint: To apply the method of sectionsâ¦ Cut 6, to the right of joints and :,. But, if we were looking at the equilibrium around joint A, the force $F_{AB}$ would push in the other direction (to the left). >>When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Tension forces always pull away from joints and members, compression forces always push towards joints and members. This contains 17 Multiple Choice Questions for Civil Engineering (CE) Test: Method Of Joints And Sections (mcq) to study with solutions a complete question bank. As the name suggests we need to consider an entire section instead of joints. We will be focused here with the method of joints with the help of this post and further we will see method of sections in our next post. Your email address will not be published. The Method of Sections involves analytically cutting the truss into sections and solving for static equilibrium for each section. Required fields are marked *, Analysis of Truss-Method of Sections and Joints. It works by cutting through the whole truss at a single section and using global equilibrium (3 equations in 2D) to solve for the unknown axial forces in â¦ The information on this website, including all content, images, code, or example problems may not be copied or reproduced in any form, except those permitted by fair use or fair dealing, without the permission of the author (except where it is stated explicitly). Even If Meaning In Kannada, Role Play Assessment Example, Acc Nz Lump Sum Payment, Introduction To Medicine Online Course, Kurt Cobain Signature Guitar, Where To Buy Frozen Mackerel Fish Near Me, Vodka And Sparkling Apple Cider, Intra Group Competition Definition, Subaru Wrx 2015 Price Used, What Is The Difference Between Osha And Msha, Knitting Pattern Books, " /> >When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Use a free body diagram (FBD) of the cut piece to solve for the unknown internal axial forces in the members that cross the cut. Why corner columns have higher values of moments than other columns? Method of section is very useful when you want to know the forces acting on a certain member in a truss. Method of joints We can determine the forces in all the members of the truss by using the method of joints. Let us consider the same diagram as before. The section must cut completely through the truss and should cut through no more than three members. Resources for Structural Engineers and Engineering Students. Classification of Bridges-Types, Span, Functions and Construction. THE METHOD OF JOINTS (Section 6.2) When using the method of joints to solve for the forces in truss members, the equilibrium of a joint (pin) is considered. The method of sections is often utilized when we want to know the forces in just a few members of a complex truss. The method centers on the joints or connection points between the members, and it is usually the fastest and easiest way to solve â¦ That is, you need to work from the sides towards the center of the truss. Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. www.spoonfeedme.com.au spoonfeedme.com.au more videos available at www.spoonfeedme.com.au P-424, determine the force in BF by the method of joints and then check this result using the method of sections. The primary benefit of the method of sections is that, for a determinate truss, you can find the force in any individual member quickly without having to solve through the entire truss one joint at a time (which you must do when using the method of joints). joints in a certain order. Then move to the next joint and find the forces in the members.Repeat the procedure and find all the member forces. This includes all external forces (including support reactions) as well as the forces acting in the members. Method of joints are the common method for the analysis of truss members.The basic concept that is used in the analysis is ,since the truss is in equilibrium the each joints in the truss is also in equilibrium, The steps for the determination of member forces, For the determination of reaction forces , we can use two equilibrium equations that is, Now we got two reactions,then choose a joint which has 2 unknown forces so as to find the two unknown forces from the two reaction we got, Take the joints and apply equations of equilibrium on that joint and find the member forces. Below is an example that is solved using both of these methods. So, we will start with section b-b to find $F_{AB}$ which we will then use in section a-a to find the forces in the other three members. It makes sense to choose this side because it does not have any external forces and it has only one reaction component $I_y$. For this problem, one way to do this is by cutting at section b-b as shown in FigureÂ 3.9. This is a simple truss that is simply supported (with pin at one end and a roller at the other). This section shares member AB with the other section a-a. For a simpler problem, only one cut would be needed if the section had only three members crossing the cut. Which one is the best for RCC concrete, M-sand or river sand? What is the biggest cost in the construction industry today? Trusses: Method of Sections Frame 19-1 *Introduction In the preceding unit you learned some general facts about trusses as well as a method of solution called the "Method of Joints." Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. For the truss shown in Fig. The sections are obtained by cutting through some of the members of the truss to expose the force inside the members. Method of Sections. Thus both the methods are used for the same purpose. The method involves breaking the truss down into individual sections and analyzing each section as a separate rigid body. This method permits us to solve directly any member by analyzing the left or the right section of the cutting plane. This section was chosen deliberately because the other three forces ($F_{BG}$, $F_{EG}$, and $F_{GH}$) all point direction through point G. So, if we evaluate the moment equilibrium about point G, we can solve directly for $F_{AB}$: which is negative, meaning that the member is actually in compression. For this problem, as previously described, we need to make two cuts and solve the equilibrium equations twice: once to find the force in member AB using section b-b and again to find the rest of the forces in the other members that cross section a-a. Joints and Sections Theory of Structure - I Lecture Outlines Method of Joints. the number of members is less than the required members.So there will be chance to fail the structure. There is also no internal instability, and therefore the truss is stable. They are used to span greater distances and to carry larger loads than can be done effectively by a single beam or â¦ All of the unknown member forces across the cut are shown, and are assumed to be in tension (pulling away from the member). As before, even though points A and F are not within the section cut, they are left in the diagram as reference points. The remaining unknowns may be found using vertical and horizontal equilibrium: The information on this website is provided without warantee or guarantee of the accuracy of the contents. In the Method of Joints, we are dealing with static equilibrium at a point. What will happen to a steel frame overloaded at bolt? The first diagram below is the presented problem for which we need to find the truss element forces. The author shall not be liable to any viewer of this site or any third party for any damages arising from the use of this site, whether direct or indirect. Since there are only three global equilibrium equations, we can only solve for three unknown member axial forces at a time using the method of sections. Step 1: Calculate the Reactions at the Supports. Truss: Method of. To do this, we need to find a way to cut the truss such that we include one of the unknown forces from a-a, but which is also cut in a way that we can directly solve for that unknown force. Newton's Third Law indicates that the â¦ Figure 1. View 04 Truss- Method of Joints and Sections.ppt from CIVIL ENGI 501 at U.E.T Taxila. That is, you need to work from the sides towards the center of the truss. Hint: To apply the method of sectionsâ¦ Cut 6, to the right of joints and :,. But, if we were looking at the equilibrium around joint A, the force $F_{AB}$ would push in the other direction (to the left). >>When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Tension forces always pull away from joints and members, compression forces always push towards joints and members. This contains 17 Multiple Choice Questions for Civil Engineering (CE) Test: Method Of Joints And Sections (mcq) to study with solutions a complete question bank. As the name suggests we need to consider an entire section instead of joints. We will be focused here with the method of joints with the help of this post and further we will see method of sections in our next post. Your email address will not be published. The Method of Sections involves analytically cutting the truss into sections and solving for static equilibrium for each section. Required fields are marked *, Analysis of Truss-Method of Sections and Joints. It works by cutting through the whole truss at a single section and using global equilibrium (3 equations in 2D) to solve for the unknown axial forces in â¦ The information on this website, including all content, images, code, or example problems may not be copied or reproduced in any form, except those permitted by fair use or fair dealing, without the permission of the author (except where it is stated explicitly). Even If Meaning In Kannada, Role Play Assessment Example, Acc Nz Lump Sum Payment, Introduction To Medicine Online Course, Kurt Cobain Signature Guitar, Where To Buy Frozen Mackerel Fish Near Me, Vodka And Sparkling Apple Cider, Intra Group Competition Definition, Subaru Wrx 2015 Price Used, What Is The Difference Between Osha And Msha, Knitting Pattern Books, " />

# method of joints and sections

Calculate the reactions at the support. Since only two equations are involved, only two unknowns can be solved for at a time. Reasons for Stirrup ends (in columns and beams) bent into a hook shape. The Method of Sections involves analytically cutting the truss into sections and solving for static equilibrium for each section. m=2j+3 then it is statically determinate,it means it is a stable structure.The number of members to keep in stable position is equal. This will make the equilibrium equations less complicated. All forces acting at the joint are shown in a FBD. Although joint G is not within the cut section, it is left in the drawing as a reference point for the moment equilibrium. Method of Sections Procedure for analysis- the following is a procedure for analyzing a truss using the method of sections: 1. The free body diagram for the cut section to the right of section b-b is shown in FigureÂ 3.10. Method of Sections In this method, we will cut the truss into two sections by passing a cutting plane through the members whose internal forces we wish to determine. Method of section is very useful when you want to know the forces acting on a certain member in a truss. Note that the right arrow ($\rightarrow$) here is relative to the cut member end. There are 2 commonly used methods to find the truss element forces, namely the Method of Joints and the Method of Sections. Reference [1] SkyCiv Cloud Engineering Software. The free body diagram for the cut section to the right of section b-b is shown in FigureÂ 3.11. 4 years ago - 335,885 views . joints in a certain order. This is because the other three members at that cut (BD, EG, and GH) are all coincident through point G. This means that if we take a moment equilibrium around point G, then none of these member forces will contribute to the equilibrium, leaving only the force in AB, which can then be found easily. For section cut b-b, we will look at the piece of the structure to the right of cut b-b as shown in FigureÂ 3.10. What are the softwares a civil engineer wants to know? They are used to span greater distances and to carry larger loads than can be done effectively by a single beam or column. By making a "cut" along the truss and member you want to calculate, you can solve for the forces without having to calculate the forces in each member, but instead calculate the forces in all members that were "cut". For finding forces in few of the specific members method of joints is preferrable. >>When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Use a free body diagram (FBD) of the cut piece to solve for the unknown internal axial forces in the members that cross the cut. Why corner columns have higher values of moments than other columns? Method of section is very useful when you want to know the forces acting on a certain member in a truss. Method of joints We can determine the forces in all the members of the truss by using the method of joints. Let us consider the same diagram as before. The section must cut completely through the truss and should cut through no more than three members. Resources for Structural Engineers and Engineering Students. Classification of Bridges-Types, Span, Functions and Construction. THE METHOD OF JOINTS (Section 6.2) When using the method of joints to solve for the forces in truss members, the equilibrium of a joint (pin) is considered. The method of sections is often utilized when we want to know the forces in just a few members of a complex truss. The method centers on the joints or connection points between the members, and it is usually the fastest and easiest way to solve â¦ That is, you need to work from the sides towards the center of the truss. Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. www.spoonfeedme.com.au spoonfeedme.com.au more videos available at www.spoonfeedme.com.au P-424, determine the force in BF by the method of joints and then check this result using the method of sections. The primary benefit of the method of sections is that, for a determinate truss, you can find the force in any individual member quickly without having to solve through the entire truss one joint at a time (which you must do when using the method of joints). joints in a certain order. Then move to the next joint and find the forces in the members.Repeat the procedure and find all the member forces. This includes all external forces (including support reactions) as well as the forces acting in the members. Method of joints are the common method for the analysis of truss members.The basic concept that is used in the analysis is ,since the truss is in equilibrium the each joints in the truss is also in equilibrium, The steps for the determination of member forces, For the determination of reaction forces , we can use two equilibrium equations that is, Now we got two reactions,then choose a joint which has 2 unknown forces so as to find the two unknown forces from the two reaction we got, Take the joints and apply equations of equilibrium on that joint and find the member forces. Below is an example that is solved using both of these methods. So, we will start with section b-b to find $F_{AB}$ which we will then use in section a-a to find the forces in the other three members. It makes sense to choose this side because it does not have any external forces and it has only one reaction component $I_y$. For this problem, one way to do this is by cutting at section b-b as shown in FigureÂ 3.9. This is a simple truss that is simply supported (with pin at one end and a roller at the other). This section shares member AB with the other section a-a. For a simpler problem, only one cut would be needed if the section had only three members crossing the cut. Which one is the best for RCC concrete, M-sand or river sand? What is the biggest cost in the construction industry today? Trusses: Method of Sections Frame 19-1 *Introduction In the preceding unit you learned some general facts about trusses as well as a method of solution called the "Method of Joints." Trusses: Method of Joints Frame 18-1 *Introduction A truss is a structure composed of several members joined at their ends so as to form a rigid body. For the truss shown in Fig. The sections are obtained by cutting through some of the members of the truss to expose the force inside the members. Method of Sections. Thus both the methods are used for the same purpose. The method involves breaking the truss down into individual sections and analyzing each section as a separate rigid body. This method permits us to solve directly any member by analyzing the left or the right section of the cutting plane. This section was chosen deliberately because the other three forces ($F_{BG}$, $F_{EG}$, and $F_{GH}$) all point direction through point G. So, if we evaluate the moment equilibrium about point G, we can solve directly for $F_{AB}$: which is negative, meaning that the member is actually in compression. For this problem, as previously described, we need to make two cuts and solve the equilibrium equations twice: once to find the force in member AB using section b-b and again to find the rest of the forces in the other members that cross section a-a. Joints and Sections Theory of Structure - I Lecture Outlines Method of Joints. the number of members is less than the required members.So there will be chance to fail the structure. There is also no internal instability, and therefore the truss is stable. They are used to span greater distances and to carry larger loads than can be done effectively by a single beam or â¦ All of the unknown member forces across the cut are shown, and are assumed to be in tension (pulling away from the member). As before, even though points A and F are not within the section cut, they are left in the diagram as reference points. The remaining unknowns may be found using vertical and horizontal equilibrium: The information on this website is provided without warantee or guarantee of the accuracy of the contents. In the Method of Joints, we are dealing with static equilibrium at a point. What will happen to a steel frame overloaded at bolt? The first diagram below is the presented problem for which we need to find the truss element forces. The author shall not be liable to any viewer of this site or any third party for any damages arising from the use of this site, whether direct or indirect. Since there are only three global equilibrium equations, we can only solve for three unknown member axial forces at a time using the method of sections. Step 1: Calculate the Reactions at the Supports. Truss: Method of. To do this, we need to find a way to cut the truss such that we include one of the unknown forces from a-a, but which is also cut in a way that we can directly solve for that unknown force. Newton's Third Law indicates that the â¦ Figure 1. View 04 Truss- Method of Joints and Sections.ppt from CIVIL ENGI 501 at U.E.T Taxila. That is, you need to work from the sides towards the center of the truss. Hint: To apply the method of sectionsâ¦ Cut 6, to the right of joints and :,. But, if we were looking at the equilibrium around joint A, the force $F_{AB}$ would push in the other direction (to the left). >>When you're done reading this section, check your understanding with the interactive quiz at the bottom of the page. Tension forces always pull away from joints and members, compression forces always push towards joints and members. This contains 17 Multiple Choice Questions for Civil Engineering (CE) Test: Method Of Joints And Sections (mcq) to study with solutions a complete question bank. As the name suggests we need to consider an entire section instead of joints. We will be focused here with the method of joints with the help of this post and further we will see method of sections in our next post. Your email address will not be published. The Method of Sections involves analytically cutting the truss into sections and solving for static equilibrium for each section. Required fields are marked *, Analysis of Truss-Method of Sections and Joints. It works by cutting through the whole truss at a single section and using global equilibrium (3 equations in 2D) to solve for the unknown axial forces in â¦ The information on this website, including all content, images, code, or example problems may not be copied or reproduced in any form, except those permitted by fair use or fair dealing, without the permission of the author (except where it is stated explicitly).


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# Time Reversal, CPT, spin-statistics, mass gap and chirality of Euclidean fermion field theory

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In Minkowski space even-dim (say $d+1$ D) spacetime dimension, we can write fermion-field theory as the Lagrangian:

$$\mathcal{L}=\bar{\psi} (i\not \partial-m)\psi+ \bar{\psi} \phi_1 \psi+\bar{\psi} (i \gamma^5)\phi_2 \psi$$

with Yukawa coupling to scalar term (with $\phi_1$) and pseudoscalar term (with $\phi_2$). Here $\bar{\psi}=\psi^\dagger\gamma^0$. This $\mathcal{L}$ is:

(i) Hermitian

(ii) invariant under Lorentz group SO($d,1$).

In the Euclidean fermion field theory, there are many attempts in the literature to find an analytic continuation from Minkowski to Euclidean field theory, and to satisfy the conditions of:

(i) Hermitian

(ii) invariant under rotational group SO($d+1$)

for example, in Steven Weinberg Vol II, $$\mathcal{L}_E= \psi^\dagger(i\not \partial_E-m)\psi$$

or this PRL paper,

$$\mathcal{L}_E= \psi^\dagger i \gamma^E_5(i\not \partial_E-m)\psi$$

in the case of this PRL paper, $\gamma^E_0=i \gamma_5$, $\gamma^E_5=-i \gamma_0$, and $\gamma^E_j=\gamma^E_j$ for $j=1,2,\dots$

The clifford algebra: ${\gamma_\mu,\gamma_\nu}=2(+,-,-,-,\dots)$, then $${\gamma^E_\mu,\gamma^E_\nu}=2(-,-,-,-,\dots)$$ with $x_E=(t_E,x_1,x_2,x_3,\dots)$

I wonder in the Euclidean fermion field theory:

(Q1) Time Reversal and CPT: how does the Time Reversal $T$ work in Euclidean theory, say $T_E$? Is time reversal $T_E$ the same as parity operator $P$ then? Is $T_E$ unitary or anti-unitary? And whether there is CPT theorem still? If partity $P$ and time reversal $T_E$ operators are (almost) the same meaning in Euclidean space, then how CPT theorem in Euclidean field theory version becomes?

(Q2) spin and spin-statistics:

In Minkowski signature, although spin state does not change under parity $P$, but the spin state changes under time reversal $T$ - spin flips direction, (see, for example, Peskin and Schroeder QFT p.68), say in 4D (d+1=4),

$$\xi^s \to (-i \sigma_2)(\xi^s)^* \equiv \xi^{-s}$$

Flip spin twice and measuring the spin eigenvalue by $(\vec{n} \cdot \vec{\sigma})$,

$$(\vec{n} \cdot \vec{\sigma}) \xi^s = s \xi^s \to \\ (\vec{n} \cdot \vec{\sigma}) (-i \sigma_2 )\big((-i \sigma_2 )(\xi^s)^*\big)^* = (\vec{n} \cdot \vec{\sigma}) (\mathbf{(-1)}\xi^s) = s (\mathbf{(-1)}\xi^s)$$

will give the same eigenvalue of $s$, but the statefunction picks up a (-1) sign. This is related to spin-statistics theorem of fermions.

In Euclidean signature, whether there is a defined notion of spin? Does spin state change under parity $P$ and time reversal $T_E$? Is there any kind of spin-statistics theorem in Euclidean signature?

(Q3) pseudoscalar:

In Minkowski, we have a Hermitian pseudoscalar term $\mathcal{L}_{M,pseudo}=\bar{\psi} (i \gamma^5) \psi$,

with:

$$P \mathcal{L}_{M,pseudo} \psi P= -\mathcal{L}_{M,pseudo}$$

$$T \mathcal{L}_{M,pseudo} \psi T= -\mathcal{L}_{M,pseudo}$$

$$C \mathcal{L}_{M,pseudo} C= +\mathcal{L}_{M,pseudo}$$

In Euclidean space, is there a peudoscalar term $\mathcal{L}_{E,pseudo}$ in the version of this Euclidean theory: $\mathcal{L}_E=\psi^\dagger i \gamma^E_5(i\not \partial_E-m)\psi$, such that $\mathcal{L}_{E,pseudo}$ is Hermitian and SO(d+1) rotational invariance, and with

$$P \mathcal{L}_{E,pseudo} \psi P= -\mathcal{L}_{E,pseudo}$$

$$T_E \mathcal{L}_{E,pseudo} \psi T_E= -\mathcal{L}_{E,pseudo}$$

$$C \mathcal{L}_{E,pseudo} C= +\mathcal{L}_{E,pseudo}$$

what is $\mathcal{L}_{E,pseudo}=?$ in the case of 2D (d+1=2) and 4D (d+1=4)?

(Q4) mass gap and chirality:

In Minkowski theory, the mass gap is due to the term:

$$\mathcal{L}_{M,mass}=m \bar{\psi}\psi= m (\psi_L^\dagger \psi_R+\psi_R^\dagger \psi_L)$$

where $\psi_L,\psi_R$ interpreted as massless limit of Left-, Right-handed Weyl spinors.

In Euclidean theory, however, in Steven Weinberg QFT II's theory, the mass term is written as $m \psi^\dagger \psi$, does that mean

$$\mathcal{L}_{E,mass}=m \psi^\dagger \psi=m (\psi_L^\dagger \psi_L+\psi_R^\dagger \psi_R)$$

the mass gap is generated from a forward scattering term( $L\to L, R\to R$)? (This is weird!) Or does the projection $P_L, P_R$ and chirality is defined differently in Euclidean theory? How does this projection $P_L, P_R$ reflect the group structure of

$$SO(4) \simeq SU(2) \times SU(2)/Z_2 \text{ in the case of 4D} (d+1=4)?$$

This post imported from StackExchange Physics at 2014-06-04 11:36 (UCT), posted by SE-user Idear
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# Exercise 3.7: Synchronous Demodulator

The spectral functions  $R(f)$  and  $Z_{\rm E}(f)$

To reset an amplitude-modulated signal to the original frequency range, a  "Synchronous Demodulator"  is often used:

• This multiplies the AM input signal  $r(t)$  with a carrier signal  $z_{\rm E}(t)$  on the receiver side, which should match the carrier signal  $z_{\rm S}(t)$  on the transmitter side with regard to both frequency  $f_{\rm T}$  and phase  $\varphi_{\rm T}$.
• This is followed by a rectangular low-pass filter to eliminate all spectral components above the carrier frequency  $f_{\rm T}$.  We call the output signal of the synchronous demodulator  $v(t)$.

The spectrum  $R(f)$  of the received signal  $r(t)$  sketched above is produced by  "Two-sideband Amplitude Modulation"  of a sinusoidal source signal  $q(t)$  with the frequency  $5\,\text{kHz}$  and the amplitude  $8\,\text{V}$.  A cosine signal  $z_{\rm S}(t)$  with the frequency  $30\,\text{kHz}$  was used as the transmission-side carrier signal.

The spectrum of the carrier signal  $z_{\rm E}(t)$  on the receiver side consists of two Dirac lines according to the sketch below, each with the weight  $A/2$.  Since  $z_{\rm E}(t)$  is not to contain a unit, the weights of the Dirac functions are also dimensionless.

Hints:

### Questions

1

Let $f_{\rm T} = 30\,\text{kHz}$  and  $A=1$.  Calculate the output signal  $v(t)$.
What signal value occurs at time  $t = 50\, {\rm µ} \text{s}$?

 $v(t = 50\, µ\text{s})\ = \$  $\text{V}$

2

How large must the amplitude of the carrier signal  $z_{\rm E}(t)$  on the receiver side be chosen so that  $v(t) = q(t)$  is valid?

 $A\ = \$

3

Calculate the output signal  $v(t)$  under the conditions  $A = 2$  and $f_{\rm T} = 31\,\text{kHz}$.
What signal value occurs at time  $t = 50\, µ\text{s}$?

 $v(t = 50\, µ\text{s})\ = \$  $\text{V}$

### Solution

#### Solution

(1)  If we name the signal after the multiplier with  $m(t) = r(t) \cdot z_{\rm E}(t)$, the corresponding spectrum  $M(f)$  is the convolution product of  $R(f)$  and  $Z_{\rm E}(f)$.

• Convolution of the spectrum  $R(f)$  with the right Dirac line at  $+30 \text{ kHz}$  leads to discrete spectral lines at  $-\hspace{-0.08cm}5\, \text{kHz}$,  $+5 \,\text{kHz}$,  $+55 \,\text{kHz}$  and  $+65 \,\text{kHz}$.  These are all imaginary and smaller than the impulse weights of  $R(f)$  by a factor of  $A/2 = 0.5$.
• Convolution of  $R(f)$  with the Dirac at  $-\hspace{-0.08cm}30 \,\text{kHz}$  yields lines at  $-\hspace{-0.08cm}65 \,\text{kHz}$,  $-55 \,\text{kHz}$, $-5 \,\text{kHz}$  and  $+5 \,\text{kHz}$.

By superimposing the two intermediate results and taking into account the low-pass filter, which suppresses the lines at  $\pm 55 \text{ kHz}$  and  $\pm 65 \text{ kHz}$ , it thus follows for the spectrum of the sink signal:

$$V( f) = - {\rm{j}} \cdot 2\;{\rm{V}} \cdot \delta ( {f - f_{\rm N} }) + {\rm{j}} \cdot 2\;{\rm{V}} \cdot \delta ( {f + f_{\rm N} } )\hspace{0.3cm}{\rm with}\hspace{0.3cm}f_{\rm N} = 5\;{\rm kHz}.$$
• The sink signal  $v(t)$  is therefore a  $5 \text{ kHz}$–sine signal with amplitude  $4 \text{ V}$.
• The time  $t = 50\, µ\text{s}$  corresponds to a quarter of the period  $T_0 = 1/f_{\rm N} = 200\, µ\text{s}$.
• Thus the sink signal is maximum here, i.e.  $\underline{4 \text{ V}}$.

(2)  With  $A = 1$  the sink signal   $v(t)$  is only half as large as  $q(t)$   ⇒   With  $\underline{A = 2}$  both signals would be equal.

(3)  The Dirac lines at  $\pm f_{\rm T}$  each have weight  $1$.  All spectral lines mentioned below are imaginary and equal in magnitude to  $2 \text{ V}$.

• The convolution of  $R(f)$  with the right Diracl ine of  $z_{\rm E}(t)$  yields components at  $-\hspace{-0.08cm}4\, \text{kHz (p: positive)}$,  $+6 \,\text{kHz (n: negative)}$, $+56 \,\text{kHz (p)}$  and  $+66 \,\text{kHz (n)}$.
• In contrast, the convolution with the left Dirac function leads to spectral lines at  $-\hspace{-0.08cm}66 \,\text{kHz (p)}$,  $-\hspace{-0.08cm}56 \,\text{kHz (n)}$,  $-\hspace{-0.08cm}6 \,\text{kHz (p)}$  und  $+4 \,\text{kHz (n)}$, all also with the (magnitude-related) impulse weights  $2 \text{ V}$.
• Taking the low–pass into account, there are only the four spectral lines at  $\pm 4 \,\text{kHz}$  and  $\pm 6 \,\text{kHz}$.
• The associated time signal is thus with  $f_4 = 4 \,\text{kHz}$  and  $f_6 = 6 \,\text{kHz}$:
$$v( t ) = 4\;{\rm{V}} \cdot \sin ( {2{\rm{\pi }}f_4 t} ) + 4\;{\rm{V}} \cdot \sin ( {2{\rm{\pi }}f_6 t} ) \ne q( t ) = 8\;{\rm{V}} \cdot \sin ( {2{\rm{\pi }}f_5 t} ).$$
• At time  $t = 50\, µ\text{s}$  one obtains:
$$v( t = 50\, µ\text{s}) = 4\;{\rm{V}} \cdot \big[ {\sin \big ( {0.4{\rm{\pi }}} ) + \sin ( {0.6{\rm{\pi }}} )} \big]\hspace{0.15 cm}\underline{ = 7.608\;{\rm{V}}}{\rm{.}}$$


text:
# Angle Help Please

Printable View

• Apr 23rd 2008, 05:36 PM
stellina_91
Angle Help Please
Find a in the diagram below, giving all reasons.

Could someone please help me with this question. I have no idea where to start!

Thanks.
• Apr 23rd 2008, 10:02 PM
Soroban
Hello, stellina_91!

I assume that $EFHD$ is a straight line.

In $\Delta CFD\!:\;\angle EFI$ is an exterior angle.
. . Hence: . $\angle EFI \:=\:\angle C + \angle D \:=\:20^o + 35^o \quad\Rightarrow\quad \angle EFI\:=\:55^o$

In $\Delta AIB\!:\;\angle EIF$ is an exterior angle.
. . Hence: . $\angle EIF \:=\:\angle A + \angle B \:=\:45^o + 30^o\quad\Rightarrow\quad\angle EIF = 75^o$

In $\Delta IEF\!:\;a \:=\:\angle IEF \:=\:180^o - 55^o - 75^o \quad\Rightarrow\quad\boxed{ a\;=\;50^o}$

• Apr 24th 2008, 10:25 AM
gdbaillargeon
Quote:

Originally Posted by stellina_91
Find a in the diagram below, giving all reasons.

Could someone please help me with this question. I have no idea where to start!

Thanks.

The first thing is to realize that in each triangle shown all the angles will add up to 180 degrees. Start there and remember the adjacent opposite angles are equal


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# Lyme disease is caused by a bacterium transmitted to humans

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Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that

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Why option B is wrong
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This is a very interesting and somewhat tricky question. Here is my analysis of this question.

Bacteria -> whitefooted mice -> larvae of deer ticks -> humans
Larvae also feed on 'other species' which do not harbor the bacterium.

Conclusion: Increase the population of 'other species'; fewer people will get Lyme disease.

Strengthen the conclusion:

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.

Out of scope.

B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.

Out of scope. Argument doesn't discuss whether humans can directly contract Lyme disease. The argument only deals with Lyme disease through deer ticks. Let me elaborate on this. Say 100 people contract Lyme disease every year. At least some of them are through infected deer ticks. If number of infected deer ticks is reduced, the number of infected humans will reduce too. It is immaterial whether there are other ways of contracting lyme disease. If all 100 humans get infected through deer ticks, the number of infected humans might go down to 50. If half get infected directly and half through deer ticks, number of infected humans may go down to 75. In any case, we do expect the number of humans infected to go down. Hence, we can say that option (B) has no relevance as far as our conclusion goes. We are only concluding that there will be a decrease - not the amount of decrease.

C. A deer tick feeds only once while in the larval stage.
If there are more uninfected food sources, it is likely that when the larvae feed, they feed on uninfected food. If the larvae do not feed again, it is probable that they will not carry the bacterium of Lyme disease and hence fewer humans will get affected. Answer (C)

D. A single host animal can be the source of bacteria for many tick larvae.
It doesn't strengthen our plan since bacteria could still proliferate if a single host can be source for many tick larvae. So we may not see much decrease in Lyme disease in humans.

E. None of the other species on which deer tick larvae feed harbor other bacteria that
ticks transmit to humans.

Out of scope.
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Current Student Joined: 28 Apr 2012 Posts: 306 Location: India Concentration: Finance, Technology GMAT 1: 650 Q48 V31 GMAT 2: 770 Q50 V47 WE: Information Technology (Computer Software) Followers: 29 Kudos [?]: 410 [2] , given: 142 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Feb 2013, 00:07 2 This post received KUDOS X disease -> to humans -> from deer ticks. larva deer ticks -> from feeding white footed mice (culprit) Other food sources of "deer ticks" do not cause infection. So if other food sources are increased, "deer ticks" would feed on them and refrain from feeding white footed mice. What if, deer tick larva feeds both on white footed mice and alternative source ? My conclusion won't be valid in that case. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. I am not bothered about suffering if ticks B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. Does not help. Number of white-footed mice remain same before/after increased other food sources for larvae. Humans would be benefited by decreased infected ticks. C. A deer tick feeds only once while in the larval stage. If deer ticks feed only once in larval stage and they have abundant infect free sources, then there will be less infected ticks and our conclusion that humans will be safer holds valid. D. A single host animal can be the source of bacteria for many tick larvae. That is possible, but we are not concerned on number of mice. If alternative food sources are availble, atleast some ticks would be non-infected. E. None of the other species on which deer tick larvae feed harbor other bacteria already clarified in the premise, " certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species " _________________ "Appreciation is a wonderful thing. It makes what is excellent in others belong to us as well." ― Voltaire Press Kudos, if I have helped. Thanks! e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [1] , given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 25 Feb 2013, 23:08 1 This post received KUDOS Expert's post monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, I'll just focus on your question that why B is incorrect. Let's first identify the conclusion: Conclusion: if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. So, this is a causal argument i.e. an argument which says that if you do X, you'll achieve Y. In this specific case, it says IF population of these other species were increased (X), then, 1. the number of ticks acquiring the bacterium would likely decline(Y) 2. and hence the number of people contracting Lyme disease would likely decline (Z) A strengthener is a statement which increases our belief in the conclusion. Let's look at option B to find out if it does so. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. It means that humans cannot directly acquire Lyme disease through white-footed mouse. But how does it affect the conclusion? If one of the ways of acquiring a disease is reduced, it should lead to a "decline" in the incidence of disease, irrespective of the fact that there are other ways to acquire a disease. For example: If a disease X can be acquired through two mediums: A and B. If I decrease A, then it should lead to a decline in X, irrespective of the fact that there are other ways to acquire the disease. However, there is a catch. If the conclusion had stated that the disease will be eliminated, then in that case I would need to consider whether there are other ways to acquire the disease or not. Hope this helps Let me know if you have any further queries. Thanks, Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [1] , given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 20 Mar 2013, 23:57 1 This post received KUDOS Expert's post 1 This post was BOOKMARKED monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, Here is the detailed analysis of this question. Understanding the Passage Premises: 1. Lyme disease is caused in humans by DT (Deer Ticks) 2. DT pick up the bacteria in the larva stage by feeding on infected WFM (White Footed Mice) 3. DT also eats other species which don't have bacteria So, (conclusion) if we increase these OS (other species), the number of DT with bacteria will reduce and this will lead to reduction in the number of incidence of disease in humans. Can you understand how the conclusion is drawn? Let's understand it. DT eats OS and WFM. For illustration, let's suppose there are 50 OS and 50 WFM. In such a scenario, the probability of a DT eating WFM is 50%. Now, suppose we increase the number of OS to 450, then we have total of 500 eatables out of which only 10% are WFM, so now the probability of DT eating WFM has come down to 10%. Therefore, if we increase OS without increasing WFM, the number of DT acquiring bacteria should reduce. This is the conclusion. Prethinking Here, let's think of an assumption built in the above conclusion. It's a bit difficult if you are not very comfortable with random events and probabilities. The assumption is that DT does not have a preference of eating WFM over OS because if DT does have a preference, then even if we increase OS, DT will still eat WFM as long as WFM exists. Thus, for our conclusion to hold, this assumption is required. For people familiar with random events and probability, read this; other can skip directly to Analysis of Option statements Look at the example we took above in which we said that increasing OS to 450 and keeping WFM at 50 will make the probability of eating WFM 10%. This is based on the assumption that eating by DT is a random event or in other words, DT eats randomly whatever is lying in front of it. If we keep more OS, then the probability of eating OS will increase. However, if eating by DT is not a random event and is rather skewed towards certain possibilities, then increasing OS might not help. Analysis of option statements Before marching on, remember that we are here to find a strengthener to the conclusion that increase OS will lead to lesser DT acquring bacteria and eventually lesser humans acquiring the disease A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. - Whether they suffer or not, it doesn't matter. They make us (humans) suffer. Not relevant. Incorrect. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. - This option indicates that humans don't acquire Lyme disease directly from WFM. Let’s take the opposite and say that humans could contract Lyme disease from WFM. Now, when we increase OS, then DT will eat less of WFM. This will lead to an increase in WFM numbers. Since humans can acquire the disease directly through WFM, it would lead to increase in incidence of Lyme disease in humans. This creates doubt about the conclusion. So, this option, by indicating that humans don't acquire the disease through WFM, eliminates the doubt and hence, should be a strengthener. But there is a catch – a flaw in the above reasoning. The truth is that DT don't kill WFM and then eat them. DT are very small insects - they can't really kill mice. Like a mosquito doesn't need to kill us to feed on us. So, even if DT feeds less on WFM, it won’t lead to an increase in the numbers of WFM. Therefore, population of WFM doesn’t change on the implementation of the plan. Therefore, whether human can acquire Lyme disease directly through WFM doesn't affect the conclusion. Incorrect C. A deer tick feeds only once while in the larval stage. – This requires some understanding. Consider two scenarios: 1. Deer tick feeds only once 2. Deer tick feeds 20 times First scenario: Deer tick feeds only once Suppose we have 80 OS and 20 WFM. What is the probability of deer tick getting the bacteria? Simple. Probability = 0.2 (i.e. same as proportion of WFM) Second scenario: Deer ticks feeds 20 times. What is the probability of deer tick getting the bacteria? Remember that DT gets the bacteria even if it feeds on WFM for only once out of 20 times. So, we can say that Probability = 1 – P (DT not feeding on WFM even once) = 1 – (0.8)^20 = 1 – 0.11 = 0.89 So, what do we see? If DT eats more number of times, then even with the same proportion of OS and WFM, more DT gets bacteria. Therefore, when DT eats only once, reducing the number of WFM will have the most impact in terms of reducing the number of infected DT. Therefore, this option strengthens the conclusion. Correct. D. A single host animal can be the source of bacteria for many tick larvae. – This is fine but this will apply to both OS and WFM. If it applied to only OS, then it would strengthen our case like Option C. But since it applies to both, it doesn't impact the conclusion. Incorrect. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans – We are only concerned about bacteria related to Lyme disease. This doesn't affect the conclusion. Incorrect. Hope this helps Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com Retired Moderator Status: 2000 posts! I don't know whether I should feel great or sad about it! LOL Joined: 04 Oct 2009 Posts: 1672 Location: Peru Schools: Harvard, Stanford, Wharton, MIT & HKS (Government) WE 1: Economic research WE 2: Banking WE 3: Government: Foreign Trade and SMEs Followers: 103 Kudos [?]: 992 [0], given: 109 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 31 Mar 2012, 18:56 +1 C If the larvae feeds in a non infected species, it won't have the chance of feeding on an infected one later. _________________ "Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can." My Integrated Reasoning Logbook / Diary: http://gmatclub.com/forum/my-ir-logbook-diary-133264.html GMAT Club Premium Membership - big benefits and savings Current Student Joined: 30 Apr 2011 Posts: 15 Followers: 0 Kudos [?]: 4 [0], given: 0 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 01 Apr 2012, 14:27 metallicafan wrote: +1 C If the larvae feeds in a non infected species, it won't have the chance of feeding on an infected one later. I guess my question is how do you know they will eat the other species first? Can you elaborate on your answer? On the other hand, if you know that there no other ways to get the disease then the argument strengthens that the number of people acquiring the disease from ticks exclusively would decrease. Manager Status: Bunuel's fan! Joined: 08 Jul 2011 Posts: 233 Followers: 1 Kudos [?]: 47 [0], given: 55 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 29 Apr 2012, 11:03 This choice is incomplete. This kinda throw me off. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans. Also this is a gmat prep question. Director Joined: 03 Aug 2012 Posts: 896 Concentration: General Management, General Management GMAT 1: 630 Q47 V29 GMAT 2: 680 Q50 V32 GPA: 3.7 WE: Information Technology (Investment Banking) Followers: 24 Kudos [?]: 765 [0], given: 322 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 23 Feb 2013, 22:13 Someone please throw some light upon this one. Rgds, SA _________________ Rgds, TGC! _____________________________________________________________________ I Assisted You => KUDOS Please _____________________________________________________________________________ Senior Manager Joined: 22 Nov 2010 Posts: 285 Location: India GMAT 1: 670 Q49 V33 WE: Consulting (Telecommunications) Followers: 5 Kudos [?]: 157 [0], given: 75 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Feb 2013, 00:16 Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. [CONCLUSION] Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. OFS B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. No effect on conclusion. Although , it tries to eliminate one of the other source of disease C. A deer tick feeds only once while in the larval stage. CORRECT D. A single host animal can be the source of bacteria for many tick larvae. OFS. E. None of the other species on which deer tick larvae feed harbor other bacteria that Please provide complete option Cause & Effect: deer ticks ---feeds on infected food in the larval stage---> Lyme disease. Passage proposes to increase the number of UN-infected feeds to reduce the spread of Lyme disease. Now suppose, there are 10 infected feeds & 10 UN-infected feeds. And as per plan we increase the UN-infected feeds to 100. But if a larva feeds multiple times than even after having UN-infected feeds for 6 time (for e.g.), it haves infected feed than it will carry the bacterium that causes Lyme disease. Therefore, choice C strengthens the conclusion BY RESTRICTING THE NO. OF FEEDS IN THE LARVAL STAGE _________________ YOU CAN, IF YOU THINK YOU CAN BSchool Forum Moderator Joined: 27 Aug 2012 Posts: 1194 Followers: 134 Kudos [?]: 1615 [0], given: 144 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 02 Mar 2013, 04:16 Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. _________________ e-GMAT Representative Joined: 02 Nov 2011 Posts: 2022 Followers: 2212 Kudos [?]: 7742 [0], given: 291 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 02 Mar 2013, 10:03 debayan222 wrote: Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. Hi Debayan, Interesting doubt! Before I respond to this, can you please tell me why you think option C is correct? This would help me understand the exact source of your doubt. Thanks, Chiranjeev _________________ | '4 out of Top 5' Instructors on gmatclub | 70 point improvement guarantee | www.e-gmat.com BSchool Forum Moderator Joined: 27 Aug 2012 Posts: 1194 Followers: 134 Kudos [?]: 1615 [0], given: 144 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 19 Mar 2013, 11:54 egmat wrote: debayan222 wrote: Hi Chiranjeev, I think option B is wrong for this reason also-we need to find out the option that supports the conclusion which is all about other species and 'white footed mice' is associated with 'deer ticks' only...So this option(B) has nothing to do with 'other species'. Pleas let me know whether I got it right... It would be really helpful if you please come up with detail explanation and analysis of this question. Much appreciate your feedback. Hi Debayan, Interesting doubt! Before I respond to this, can you please tell me why you think option C is correct? This would help me understand the exact source of your doubt. Thanks, Chiranjeev Hey Chiranjeev, Sorry man for late come back...!Somehow I missed your reply and now have found it out while going through my inbox. Option C-as the feeding is only once on the active species so if the no. of inactive species is increased then the disease would likely decline. IMO-it turns out to be the best available option in this case. Awaiting your detail analysis! _________________ Manager Joined: 10 Jan 2010 Posts: 79 Schools: IIM Followers: 0 Kudos [?]: 26 [0], given: 11 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 21 Mar 2013, 10:40 egmat wrote: monikaleoster wrote: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacteria for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that Why option B is wrong Hi, Here is the detailed analysis of this question. Understanding the Passage Premises: 1. Lyme disease is caused in humans by DT (Deer Ticks) 2. DT pick up the bacteria in the larva stage by feeding on infected WFM (White Footed Mice) 3. DT also eats other species which don't have bacteria So, (conclusion) if we increase these OS (other species), the number of DT with bacteria will reduce and this will lead to reduction in the number of incidence of disease in humans. Can you understand how the conclusion is drawn? Let's understand it. DT eats OS and WFM. For illustration, let's suppose there are 50 OS and 50 WFM. In such a scenario, the probability of a DT eating WFM is 50%. Now, suppose we increase the number of OS to 450, then we have total of 500 eatables out of which only 10% are WFM, so now the probability of DT eating WFM has come down to 10%. Therefore, if we increase OS without increasing WFM, the number of DT acquiring bacteria should reduce. This is the conclusion. Prethinking Here, let's think of an assumption built in the above conclusion. It's a bit difficult if you are not very comfortable with random events and probabilities. The assumption is that DT does not have a preference of eating WFM over OS because if DT does have a preference, then even if we increase OS, DT will still eat WFM as long as WFM exists. Thus, for our conclusion to hold, this assumption is required. For people familiar with random events and probability, read this; other can skip directly to Analysis of Option statements Look at the example we took above in which we said that increasing OS to 450 and keeping WFM at 50 will make the probability of eating WFM 10%. This is based on the assumption that eating by DT is a random event or in other words, DT eats randomly whatever is lying in front of it. If we keep more OS, then the probability of eating OS will increase. However, if eating by DT is not a random event and is rather skewed towards certain possibilities, then increasing OS might not help. Analysis of option statements Before marching on, remember that we are here to find a strengthener to the conclusion that increase OS will lead to lesser DT acquring bacteria and eventually lesser humans acquiring the disease A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. - Whether they suffer or not, it doesn't matter. They make us (humans) suffer. Not relevant. Incorrect. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. - This option indicates that humans don't acquire Lyme disease directly from WFM. Let’s take the opposite and say that humans could contract Lyme disease from WFM. Now, when we increase OS, then DT will eat less of WFM. This will lead to an increase in WFM numbers. Since humans can acquire the disease directly through WFM, it would lead to increase in incidence of Lyme disease in humans. This creates doubt about the conclusion. So, this option, by indicating that humans don't acquire the disease through WFM, eliminates the doubt and hence, should be a strengthener. But there is a catch – a flaw in the above reasoning. The truth is that DT don't kill WFM and then eat them. DT are very small insects - they can't really kill mice. Like a mosquito doesn't need to kill us to feed on us. So, even if DT feeds less on WFM, it won’t lead to an increase in the numbers of WFM. Therefore, population of WFM doesn’t change on the implementation of the plan. Therefore, whether human can acquire Lyme disease directly through WFM doesn't affect the conclusion. Incorrect C. A deer tick feeds only once while in the larval stage. – This requires some understanding. Consider two scenarios: 1. Deer tick feeds only once 2. Deer tick feeds 20 times First scenario: Deer tick feeds only once Suppose we have 80 OS and 20 WFM. What is the probability of deer tick getting the bacteria? Simple. Probability = 0.2 (i.e. same as proportion of WFM) Second scenario: Deer ticks feeds 20 times. What is the probability of deer tick getting the bacteria? Remember that DT gets the bacteria even if it feeds on WFM for only once out of 20 times. So, we can say that Probability = 1 – P (DT not feeding on WFM even once) = 1 – (0.8)^20 = 1 – 0.11 = 0.89 So, what do we see? If DT eats more number of times, then even with the same proportion of OS and WFM, more DT gets bacteria. Therefore, when DT eats only once, reducing the number of WFM will have the most impact in terms of reducing the number of infected DT. Therefore, this option strengthens the conclusion. Correct. D. A single host animal can be the source of bacteria for many tick larvae. – This is fine but this will apply to both OS and WFM. If it applied to only OS, then it would strengthen our case like Option C. But since it applies to both, it doesn't impact the conclusion. Incorrect. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans – We are only concerned about bacteria related to Lyme disease. This doesn't affect the conclusion. Incorrect. Hope this helps Chiranjeev Very nice explanation, Chiranjeev. Thanks Manager Joined: 07 Feb 2011 Posts: 103 Followers: 0 Kudos [?]: 60 [0], given: 45 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Mar 2013, 04:01 VeritasPrepKarishma wrote: This is a very interesting and somewhat tricky question. Here is my analysis of this question. Bacteria -> whitefooted mice -> larvae of deer ticks -> humans Larvae also feed on 'other species' which do not harbor the bacterium. Conclusion: Increase the population of 'other species'; fewer people will get Lyme disease. Strengthen the conclusion: A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. Out of scope. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. Out of scope. Argument doesn't discuss whether humans can directly contract Lyme disease. The argument only deals with Lyme disease through deer ticks. Let me elaborate on this. Say 100 people contract Lyme disease every year. At least some of them are through infected deer ticks. If number of infected deer ticks is reduced, the number of infected humans will reduce too. It is immaterial whether there are other ways of contracting lyme disease. If all 100 humans get infected through deer ticks, the number of infected humans might go down to 50. If half get infected directly and half through deer ticks, number of infected humans may go down to 75. In any case, we do expect the number of humans infected to go down. Hence, we can say that option (B) has no relevance as far as our conclusion goes. We are only concluding that there will be a decrease - not the amount of decrease. C. A deer tick feeds only once while in the larval stage. If there are more uninfected food sources, it is likely that when the larvae feed, they feed on uninfected food. If the larvae do not feed again, it is probable that they will not carry the bacterium of Lyme disease and hence fewer humans will get affected. Answer (C) D. A single host animal can be the source of bacteria for many tick larvae. It doesn't strengthen our plan since bacteria could still proliferate if a single host can be source for many tick larvae. So we may not see much decrease in Lyme disease in humans. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans. Out of scope. Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected. I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question _________________ We appreciate your kudos' Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7370 Location: Pune, India Followers: 2285 Kudos [?]: 15093 [0], given: 224 Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink] ### Show Tags 24 Mar 2013, 20:54 manimgoindowndown wrote: Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected. I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question Actually, (B) is not even an assumption. It is out of scope and has nothing to do with our current argument. Even if 'infection by deer ticks' is just one of the ways of acquiring Lyme disease, if you decrease the number of infected deer ticks (by increasing population of other food sources), you will expect to decrease the number of infected humans. So whether there are other sources of Lyme disease infection, doesn't bother our argument at all. When will it make a difference? Consider the same argument with a different conclusion: Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline proportionally. This conclusion says that if you increase other food sources and hence, decrease the number of infected deer ticks by say 50%, number of people contracting lyme disease will decrease by 50% too. Here you are assuming that there is no other source of infection in humans and decrease in number of infected ticks might make you see proportional results. We are trying to quantify the decrease here and hence the other ways of getting infected come into play. In our original argument, all we are focusing on is that if you can control one way of getting infected, you will decrease the number of human infections. It may be the only way of getting infected or there may be other ways too. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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09 Apr 2013, 20:42
VeritasPrepKarishma wrote:
manimgoindowndown wrote:

Isn't answer B introducing a possibility which we should assume true of direct infection? Or are you saying that it introduces this but unlike the information it has given us about DT, it doesn't elaborate on how or what it does to the number of infected.

I think what might be confusing about answer B would be it would be correct if this was an assumption question, correct? But it is a strengthen question

Actually, (B) is not even an assumption. It is out of scope and has nothing to do with our current argument. Even if 'infection by deer ticks' is just one of the ways of acquiring Lyme disease, if you decrease the number of infected deer ticks (by increasing population of other food sources), you will expect to decrease the number of infected humans. So whether there are other sources of Lyme disease infection, doesn't bother our argument at all.

So you're saying that B actually decreases the number of infected humans but doesn't adress the issue of infected dear ticks because the population of infected mice is still the same?

What you said in bold is what we are tryign to strengthen, no? That less humans are infected?
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09 Apr 2013, 22:57
manimgoindowndown wrote:

So you're saying that B actually decreases the number of infected humans but doesn't adress the issue of infected dear ticks because the population of infected mice is still the same?

What you said in bold is what we are tryign to strengthen, no? That less humans are infected?

I am not sure from where you got this. (B) doesn't do anything to the number of infected humans. It only tells you that direct infection is not a source of infection in humans. That whoever gets it, doesn't get it by directly through white footed mice. It is immaterial really. All we need to focus on is the relation:

whitefooted mice -> deer ticks -> humans
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4 Lyme disease is caused by a bacterium transmitted to humans 4 15 Apr 2014, 05:13
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