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光 · 2020年01月15日

妻子收到丈夫的信一定回复?

 So why the prob of receive-response is not 100%? 我看了另一个同样的提问,但是回答还是不明白,因为没收到且没回复的概率就是100%,而不是1/3?

问题如下图:

选项:

A.

B.

C.

D.

解释:

1 个答案
已采纳答案

品职答疑小助手雍 · 2020年01月15日

emmmm这个大意是邮件可以寄到正确地址的概率是2/3,所以妻子收到信的概率是2/3,没收到是1/3。

妻子如果收到了肯定会回信,也就是在这收到信写回信的2/3里,丈夫收到信的概率是2/3(这个占总概率的4/9),没收到的概率是1/3(这个占总概率的2/9)。

妻子没收到就不会写回信,这没收到信的1/3里,丈夫100%收不到信。(这个占总概率的1/3)

那么没收到信的概率就是2/9+1/3=5/9。因为是妻子写了回信寄回去没收到的概率是2/9,所以(2/9)/(5/9)=2/5

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