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Tuesday, July 11, 2006

Answer to would you switch or not

Here is the answer given by some more smarter than I. Many mathematicians, disagree with her, Marilyn Vos Savant. Read about it here: http://www.marilynvossavant.com/articles/gameshow.html Yes; you should switch. The first door has a 1/3 chance of winning, but the second door has a 2/3 chance. Here's a good way to visualize what happened. Suppose there are a million doors, and you pick door #1. Then the host, who knows what's behind the doors and will always avoid the one with the prize, opens them all except door #777,777. You'd switch to that door pretty fast, wouldn't you?
DOOR 1 DOOR 2 DOOR 3 RESULT
GAME 1 AUTO GOAT GOAT Switch and you lose.
GAME 2 GOAT AUTO GOAT Switch and you win.
GAME 3 GOAT GOAT AUTO Switch and you win.
GAME 4 AUTO GOAT GOAT Stay and you win.
GAME 5 GOAT AUTO GOAT Stay and you lose.
GAME 6 GOAT GOAT AUTO Stay and you lose.

When you switch, you win 2/3 of the time and lose 1/3, but when you don't switch, you only win 1/3 of the time and lose 2/3. You can try it yourself and see.

Alternatively, you can actually play the game with another person acting as the host with three playing cards—two jokers for the goat and an ace for the prize. However, doing this a few hundred times to get statistically valid results can get a little tedious, so perhaps you can assign it as extra credit—or for punishment! (That'll get their goats!)

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