作者david31408 (希望你没事)
看板GRE_Verbal
标题Re: [计量] CAT (机率问题)
时间Tue Oct 14 00:22:52 2008
※ 引述《ELASTOMER (恶性循环........)》之铭言：
: 题目是
: If a bowl contains seven marbles, three red and four
: green, four marbles are drawn from the bowl at random
: without replacement. What is the propability that contains
: two red marbles and two green ones?
: 答案是18/35 不知要怎麽解,麻烦各位帮我解答一下,谢谢
问说碗内剩2,2的机率
C(3,1)*C(4,2)-->各剩下两个所以要3个拿1个 4个拿2个
-------------
C(7,3) -->7个里面总共拿3个
=3*6/(7*6*5/6)
=18/35
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