What is the probability that the other drawer contains a silver coin?

by on 2012/02/12

Question by Andy: What is the probability that the other drawer contains a silver coin?
Jenny has three cabinets, A,B,C each of which has two drawers. Each drawer contains one coin; A has two gold coins, B has two silver coins, and C has one gold and one silver coin. A cabinet is chosen at random, one drawer is opened, and a silver coin is found. What is the probability that the other drawer in that cabinet contains a silver coin?

Best answer:

Answer by Andy
1/2 and this should be clear when you represent this scenario on paper.

Since you found a silver coin in one of the drawers, that cabinet has to be B or C, because only these two cabinets can possibly contain silver coin.

Now when one of the drawers contains a silver coin, the other drawer can either have another silver (cabinet B) OR it can have a gold coin (cabinet C).

Therefore the probability of finding silver again is 1/2

Hope this helps

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