for n people, the probability that they all have different B-day is P1=(365*364*363*362*...*(365-n+1)/365^n The complimentary of it is the probability of at least two people having same B-day P2=1-P1 Here are some numbers n = 10, P2=0.1411 n = 20, P2 = 0.4437 n = 22, P2 =0.5073 n = 30, P2 =0.7305 n = 50, P2= 0.9704 www.ddhw.com Notice that for 22 people, the odds that at least two people having same B-day is greater than half. There is this famous application to a soccer match. There are 22 players on the field. The chance is better than 50% that at least two players have same B-day. If you count the three referees (25 people altogether), the chance is 0.5982. Q.E.D.
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哈哈哈哈 O(∩_∩)O哈哈~ 好久不来了，不小心看了一眼自己主页，发现自动关联了自己以往发过的帖，点进这个看了一眼，笑个半死。。。敢情我当初还发过这么搞笑的东西啊，我自己完全不记得了 
雷达卡
发表于 2009-12-25 00:08:56
