求解一道概率题

steinlala

A basket has 5 apples, one is spoiled. If Henry picked 2 apples simultaneously and at random, what is probability that the 2 selected apples will include the spoiled one.
a. 1⁄5
b. 2⁄10
c. 2⁄5
d. 1⁄2
e. 3⁄5
为什么我算的是1/5呢？我是这样算的C4 1/(C51*C4 1)
错在哪里了呢？

season5924

分母应该是5*4/2，因为两个是同时取得吧。

teddyabc

c(4,1)/c(5,2)就好了。。。

cckjenius

是2/5对吗？如果是，那就是因为同时取，就是C（5，2）啊

steinlala

哦，对的，是同时取。呵呵，谢谢啊

sayysong

1-4/5*3/4=2/5