agree~~~

本帖於 2010-04-25 08:03:23 時間, 由版主 於德利 編輯

There are 7 people and 30 days in April. Assuming distribution of birth dates is completely random, choose one person. That person's birth date does not matter. The second person has a 29/30 chance of having a different birth date. The third person has a 28/30 chance of having a different birth date than the first and second persons. Repeat until the seventh person has a 24/30 chance of having a different birth date. Multiply to get the chance that all the birth dates will be different. Subtract from 1 to get the probability that at least one birth date will be repeated.

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