GMATprep_1题数学_不在数学讨论链接里

zsx

A basket contains 5 apples, of which 1 is spoiled and
the rest are good. If Henry is to select 2 apples from the basket
simultaneously and at random, what is the probability that the 2 apples
selected will include the spoiled apple?

这一题没有给出选项。我是这么算的：C(1,1) * C(1,4) / C(2,5) * C(2,5) = 1/25.  这样算，对吗？对于这种 “simultaneously" 的排列组合题很怕。希望大家帮帮忙！谢谢！

zsx

抱歉！不知道怎么会出现这么多乱码，只是偷懒 copy & paste 了一下 。。。是这样的：

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the probability that the 2 apples selected will include the spoiled apple?

该题没有给出答案选项。我是这么考虑的：C(1,1)*C(1,4) / C(2,5)*C(2,5) = 1/25. 这样正确吗？

zsx

啊。我又考虑了一下，觉得是：C(1,1)*C(1,4)/C(2,5)=2/5. 这样对吧？

joeywei

1-[C(2,4)/C(2,5)]=2/5  这样简单点吧~

zsx

Thanks!