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标题: 一道来自manhattan的题目，望NN们来帮帮我，谢谢~ [打印本页]

作者: evelyn205205 时间: 2011-7-20 16:24
标题: 一道来自manhattan的题目，望NN们来帮帮我，谢谢~
In a room filled with 7 people, 4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. If two individuals are selected from the room at random, what is the probability that those two individuals are NOT siblings?

答案是16/21.
这道题怎么个思路做啊？

作者: bennywang2usa 时间: 2011-7-20 16:31
题目说4个人有1个兄弟姐妹，3个人有2个兄弟姐们。根据最后题干可以看出，这7个人互相有亲戚关系哦~

作者: yaner11 时间: 2011-7-20 16:58
关系是这样的：

一组： A, B,
二组： C, D,
三组： E, F, G

3*4+ 2* 2=16
7取2等于21

作者: evelyn205205 时间: 2011-7-20 17:52
谢谢啦，你的解释很清晰~

作者: evelyn205205 时间: 2011-7-20 17:57
谢谢！

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