probability question

cain

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Aug 1, 2003
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for my econometrics class, i have to solve such a problem. i know the answer as it is intuitional, hopefully one of you will be able to offer me a solution.

A customer orders a steak in a restaurant. The waiter brings three plates numbered 1, 2
and 3. Each plate has a steak. The waiter tells the person that one of the steaks is safe to
eat, but the other two steaks are tainted with mad-cow disease. The waiter asks the person
to choose a plate. The person randomly picks plate number 2. The waiter then says to the
customer ?according to restaurant policy, I cannot tell you whether the plate you have chosen
has safe meat or tainted meat, however you and I know that at least one of the plates you did
not choose has tainted meat. The famous-chef would like you to know that plate number 3
has tainted meat.?The waiter snaps his ?ngers and plate 3 is sent back to the kitchen to be
ground up and added to the tofu burgers. At this point the customer is getting a little freaked
out and decides to walk out of the restaurant. But, as the customer tries to stand up, the
waiter takes out a gun and demands that the customer try at least one bite of famous-chef?s?
wonderful steak.

Which steak should the customer try: plate 1 or plate 2? After eating the steak, what is
probability that the customer will become sick in 10 years from mad-cow disease? (You may
assume that if the customer eats tainted steak, the customer will get mad-cow disease in 10
years with probability one).
 

MacBaine

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Aug 23, 2001
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He should choose the other plate, as initially he has a 1/3 chance of winning by choosing the first plate, whereas after the third plate is removed, he will have a 1/2 chance of choosing the winning plate. It's more complicated than that but that's a simple explanation
 

cain

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Aug 1, 2003
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Originally posted by: MacBaine
He should choose the other plate, as initially he has a 1/3 chance of winning by choosing the first plate, whereas after the third plate is removed, he will have a 1/2 chance of choosing the winning plate. It's more complicated than that but that's a simple explanation

thats the faulty solution, good try though. you need to use bayes theorem probably, i just cant remember how to do it
 

furie27

Senior member
Apr 22, 2004
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I think you can use the "Let's make a deal" solution to this. Don't have the proof handy, but conditional probabilities will get you to it.