An Urn contains two white marbles and one black marble. A marble is drawn from the Urn without replacement and put aside without my seeing it. Then a second marble is drawn, and it is white. What is the probability that the unknown removed marble is white, and what is the probability that it is black? Your answer should have exactly 3 paragraphs. Make sure that the first paragraph starts with the word "difficult" and that each paragraph is separated by two new lines.
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