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Ten letters are placed in ten pre-addressed envelopes at random. What is the probability that exactly nine letters were placed in the proper envelope?
posted by steven | 12:21 AM
Now, I'm sure I am about to embarrass myself here but...It seems to me that the probability of exactly 9 letters being placed in the correct envelopes would be 0. If by stating "9" you are implying that the 10th was not placed its correct envelope.If there are 10 envelopes, which correspond perfectly to the 10 letters, then 9 can't be placed in correct envelopes unless all 10 are.
That is the correct answer!
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