Author: GuyHaworth
Date: 12:45:44 09/25/02
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Rolf, I sympathise with your confusion, but I regret that your conclusions are incorrect. I heard of the 3-door scenario some years ago and was convinced that there was no advantage in switching. However, I was wrong then. The explanation given is perfectly correct. Suppose you choose a door - let's call it 'A': the chance the car is there is 1/3. The show host then proves that the car is not behind another door - let's call it 'B'. So where's the remaining 2/3 probability? It's sitting behind door 'C'. Why does this seem odd. Because 'C' isn't a physical door, fixed before the car is driven in. Had the car been put behind the physical door, labelled 'B' above only temporarily, the host would have chosen the other door the contestant did not choose. If you still think it's 50/50, I would be happy for you to offer me those odds as the bookmaker and I would employ the 'switch strategy' throughout. Over 3N trials, I would expect to lose N times and win 2N times, a gain of N. At $1 a trial, what N would you care to specify? [ When navigating in offshore races, if the crew insist that I have my facts wrong, I pretty quickly ask them to put their money on the table. It works. ] g
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