TT-GWD-2-31

Q31:

There are 8 magazines lying on a table; 4 are fashion magazines and the other 4 are sports magazines.  If 3 magazines are to be selected at random from the 8 magazines, what is the probability that at least one of the fashion magazines will be selected?

A.     1/2

B.     2/3

C.     32/35

D.     11/12

E.      13/14

答案是E, 请问解题思路？

也就是求1－3本全都是sports magazines得概率

1－C(3,4)/C(3,8)=1-1/14=13/14

at least....

这种东西，就是求1减去全都选不出这种东西得概率。

如果把at least 换成 only 呢……？

只要算出全部不选fashion magazines 的概率,即全部选 sports magazines.的概率为C(4,3)/C(8,3)=1/14

用1减去一个都不选的概率,即1-1/14=13/14

好方法. 我的方法笨了点, 可能较容易理解.

chose 3 magazines and 'at least 1 fashion magazine.'

So F magazine 有3种选择. 1, 2 or 3 fashion magazines. 加法原则

(C44*C43+C42*C42+C43*C40)/C83=52/56=13/14