NO.PZ2023091601000009
问题如下：
In
country X, the probability that a letter sent through the postal system reaches
its destination is 2/3. Assume that each postal delivery is independent of
every other postal delivery, and assume that if a wife receives a letter from
her husband, she will certainly mail a response to her husband. Suppose a man
in country X mails a letter to his wife (also in country X) through the postal
system. If the man does not receive a response letter from his wife, what is
the probability that his wife received his letter?
选项：
A.
1/3
B.
3/5
C.
2/3
D.
2/5
解释：
这个题目答案是2/5还是1/3
，如果是2/5那么算式分母是．什么函义
