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Old 02-19-2007, 09:40 AM
Matt Matt is offline
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Join Date: Jan 2005
Location: Rochester, MN
Posts: 376
Originally Posted by Toolish View Post
Wrong as far as i see it.

They are mutually exclusive events...the outcome of the first goat being revealed does not change the second result...you have a 50% chance of being correct either way once the other doors are revealed.

With your 100 door example, once the other 98 are revealed you are still left with a 50% chance of either door being right...the fact that incorrect doors have been removed from the equation means nothing...in choosing between the final 2 doors switch or stay means nothing, the door you initially chose becomes irrelevant.
The chances that you picked the correct door out of 100 is 1/100. They then eliminate 98 incorrect ones, leaving 2 doors. At this point, there is a great chance - 99/100 - that the car is behind the 'other' door. Your original guess still has a 1/100, or 1%, chance of being correct.

Same obviously works for 3 doors. Your 'guess' has a 1/3 chance of being correct, meaning there's a 2/3 chance it's incorrect. When they eliminate an incorrect door, your chances with the original door remain at 1/3. However, the 2/3 that before were assigned to the other two doors now are assigned to the only remaining door. So you have a 2/3 chance if you switch, and the same, original 1/3 chance if you stay.
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