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标题: [讨论]涛涛31-11-30 [打印本页]

作者: angelavivi 时间: 2006-7-16 07:04 标题: [讨论]涛涛31-11-30

Q30:C

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

Answer:

答案是C，这题怎么做？？？求高手解答。

作者: smalllittle 时间: 2006-7-16 19:50

C(9,2)/C(x,2)=6/11

x=12

作者: angelavivi 时间: 2006-7-17 21:04

thanks  a lot !!!

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