PREP 17 求解

gcywang · 发表于 2010-1-7 12:52:54

如题，答案是E,我以为是B，如何解？谢谢
In a certain board game, a stack of 48 cards, 8 of which represent shares of stock, are shuffled and then placed face down. If the first 2 cards selected do not represent shares of stock, what is the probability that the third card selected will represent a share of stock?

(A) 1/8
(B) 1/6
(C) 1/5
(D) 3/23
(E) 4/23

大荣 · 发表于 2010-1-7 13:17:02

条件概率题，用定义计算。相当于做一个实验连续选3张卡，前2次选出的卡非share of stock后，剩46张，第三次有46种取法，其中8张是有利于生成取到share of stock，所以P=8/46=4/23. 选E.

gcywang · 发表于 2010-1-7 14:05:34

谢谢哇，好人有好报

PREP 17 求解

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