请教prep数学PS的17题 概率题

lemoncello

17.2311-!-item-!-187;#058&002635

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


请问各位，这题应该怎么算呢，我自己也觉得很简单，但是就是算不出来。

energyxmy

第一张第二张抽出来，最后就剩下了48-2=46张，所以答案就是8/46

sdcar2010

8/(48-2) = 4/ 23

lemoncello

那前面两张的概率不用算吗？
就是(40/48)*(39/47)*(8/46)

skyhai1981

问法不一样吧。问的是抽到share的概率，而不是第一次第二次抽到非s且第三次抽到s的概率。

lemoncello

嗯嗯 明白啦 谢谢