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标题: 一道GWD概率~ [打印本页]

作者: weiwei_zhwq 时间: 2009-6-18 15:09
标题: 一道GWD概率~

大家帮帮忙吧, 我无望的数学啊~~可以的话把公式, 步骤都写一下, 拜托拜托~~

In a stack of cards, 9 cards are blue and the rest are red. If 2 cards are to be chosen at random from the stack without replacement, the probability that the cards chosen will both be blue is 6/11. What is the number of cards in the stack?

A. 10

B. 11

C. 12

D. 15

E. 18

作者: justbp 时间: 2009-6-18 15:59

设总数为X，则

C（9 2）/ C（X 2）= 6/11

X=12

[此贴子已经被作者于2009-6-18 15:59:54编辑过]

作者: weiwei_zhwq 时间: 2009-6-18 16:46
非常感谢!!

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