Question: When Prof. Rosa asks Ben to answer a "quiz-question" in college about 3 doors of which only one has a brand new car behind it, he explains he has a chance of 33.3% of choosing the correct door. However, when Prof. Rosa opens one door and leaves Ben a new chance to choose he claims that his chances of choosing correctly have increased from 33.3% to 66.7%, but as he already knows what is behind one of the doors, the car must be behind one of the other doors. Shouldn't his chances now be 50% in stead of 66.7%?
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Chosen answer: No, the 66.7% (2/3) chance, while counter-intuitive, is correct. See here for a much more detailed and thorough explanation: http://en.wikipedia.org/wiki/Monty_Hall_problem.
Guy