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标题: prep 一道古典概率题 [打印本页]

作者: xiaolingdang 时间: 2009-12-19 07:36 标题: prep 一道古典概率题

A certain junior class has 1,000 students and a certain senior class has 800 students. Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?

答案没破解。不过希望大家能指导一下方法

作者: wydhcuy 时间: 2009-12-19 21:54

我想的是1000分之一乘以800分之一再乘以60，不知道对不对

作者: antiquarks 时间: 2009-12-21 20:52

我认为正确，从JUIOR班里挑一个有兄妹的60/1000, 则这对兄妹就确定了，只能是1/800，总共就是你说的答案了.

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