Author: Kai Lübke
Date: 04:46:53 02/18/99
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On February 18, 1999 at 07:19:43, Jouni Uski wrote: >If You select random 23 people, it's over 50% probability that two have exact >same birth day (from 365 possibility)! This seems to be against common sense. Depends on how you look at it. If you take one of them fixed, then the probability that one of the other 22 has the same birthday is of course 22/365, less than 10%. But the case here of course is the question whether *any* of them have the same birthday. So you have a probability of 22/365 for the first person's birthday to conincide with any of the others, for the second person the prob. is 21/365 (as we need not compare with #1 again), for the third 20/365 and so on. So the overall probability is (22+21+...+2+1)/365 = 253/365 >50%. --- Shep
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