[問題] 條件機率的計算
題目是這樣子的:
The probability that,on the weekday,the college will receive letters addressed to Dr.A is 1/3. Dr.A,who arrives earlier than any of his colleagues,begins the day by collecting his mail. He has told me that there is 40% chance that he will attend college today;and I have noticed that there are no letters in his pigeon hole.In view of there being no mail in his box,what is the probability that he is attending today?
http://miupix.cc/pm-6UFKAJ
圖片上面是我的想法:
令A表是他有到學校
R表示他有收到信
當他到學校時，收到信的機率就是1/3
而如果他沒到學校，就不會收到信
但解答的想法卻是下面的那樣
跟我的想法似乎相反
想問我的想法錯在哪呢？
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