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困扰很久的一道概率题,求牛人

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楼主
发表于 2008-7-12 16:41:00 | 只看该作者

困扰很久的一道概率题,求牛人

six cards numbered from 1 to 6 are placed in an empty bowl. first one card is drawn and then put back into the bowl; then a second card is drawn. if the cards are drawn at random and if the sum of the number on the cards is 8, what is the probability that one of the two cards drawn is numbered 5?

1/6;  1/5; 1/3; 2/5; 2/3

沙发
发表于 2008-7-12 16:47:00 | 只看该作者
以下是引用jinxuanye在2008-7-12 16:41:00的发言:

six cards numbered from 1 to 6 are placed in an empty bowl. first one card is drawn and then put back into the bowl; then a second card is drawn. if the cards are drawn at random and if the sum of the number on the cards is 8, what is the probability that one of the two cards drawn is numbered 5?

1/6;  1/5; 1/3; 2/5; 2/3

2/5

板凳
发表于 2008-7-12 16:49:00 | 只看该作者
符合的组合是 2 6; 6 2; 4 4; 3 5;5 3
有number 5的组合有两个
所以是 2/5
地板
发表于 2008-7-12 18:47:00 | 只看该作者

这种题把它可能的情况列举出来就可以了啊,赞成3楼的

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