标题: 数学一题 谢谢大家 [打印本页]

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作者: bettyofariN    时间: 2010-8-5 06:48     标题: 数学一题 谢谢大家

A certain junior class has 1000 students and a cetain senior 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 random from each class, what is the possibilty that the 2 students selected will be a sibiling pair.
答案 3/40000
为什么

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作者: greates    时间: 2010-8-5 20:32

C(60,1)/C(800,1)*C(1000)
分母意思是 从800人中random取一个，1000中random取一个的可能性
分子意思是 取出来的至可能是60个sibiling pair，所以是60钟可能性

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作者: bettyofariN    时间: 2010-8-6 06:35

多谢了

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