[KJL]

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I see how Baye's Theorem can be used to solve this. My point is you don't need the new information. The host could have just of easily said choose a door and you do. Instead of showing a goat he could say, would you rather have the door you chose or would you rather have the 2 doors you didn't choose. By staying you win 1/3 of the time by switching you win 2/3 of the time.

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You need to see the goat for the problem to work. While you are right that you need by switching you will win 2/3 times; you have 2 door to choose from so this is really a 1/3 chance.