作者headnobig (Actor)
看板GMAT
标题Re: [问题] GWD &PP求解
时间Tue Oct 21 09:51:23 2008
※ 引述《yyiitt1003 (小眼钢牙妹)》之铭言：
: GWD22 Q11
: 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
一共有N个球
则 蓝球的次数 C9取2 (9*8)/2 6
-------------- = ------------ = -------------- = ----
全部的次数 CN取2 (N)(N-1)/2 11
解得 N = 12
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