硬币概率问题

jackabigail

If a coin is flipped 5times,what is the probability that it will land heads up on the first 3 flips and not on the last flips?

A3/5     B1/2    C 1/5   D1/8    E 1/32

我很头疼概率题目，牛人请帮一下忙！

bigskings

你这个题目错了吧

我查了查原题是：

When flipping coin, the possibility for it to have its head facing up is ½. If a coin is flipped five times, what’s the possibility to have the head up for the first three times and not for the rest?

是the rest  而不是 the last~~~

答案是1/2的5次方！

晕~

我还按你的题目算了半天~~呵呵

jackabigail

这种题目怎么做啊？你教教我，我最讨厌排列组合还有概率题目