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:
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NO.PZ2018122801000006问题如下 In country X, the probability tha letter sent through the postsystem reaches its stination is 2/3. Assume theapostlivery is inpennt of every other postlivery, anassume thif a wife receives a letter from her husban she will certainly mail a response to her husban Suppose a man in country X mails a letter to his wife (also in country X) through the postal system. If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter? 1/3 3/5 2/3 2/5 is correct. 考点 Bayes' formul解析 (Notices: if the wife not receive the letter, she woulnot senresponse to the man.) Note: the wife receivethe letter; ¯ : the wife not receive the letter; the mreceivea response letter from his wife; ¯ : the mnot receive a response letter from his wife The question \"If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter?\" is equto figure out P( ¯ ) 考点正态分布查表 P( ¯ )= P( ¯ ) P( ¯ ) = P( ¯ )×P( ¯ | P( ¯ )×P( ¯ |A)+P( ¯ )×P( ¯ | ¯ ) 解析 题目说信可以成功寄到的概率是2/3,假设每次送信都是独立事件。同时假设妻子如果收到丈夫的信就一定会回复。问题问如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率是多少?首先丈夫没有收到回信的条件有两种情况1.丈夫的寄信丢了,就是上面那个二叉树的下面一根,概率是1/3;2.丈夫的信寄到了,但是妻子的回信寄丢了(1/3),这种情况下概率为1/3*(2/3)=2/9所以这两种情况下概率加和=1/3+2/9=5/9根据贝叶斯公式,如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率=(2/9)/(5/9)=2/5 = (2/3)×(1/3) (2/3)×(1/3)+(1/3)×1 = 2 5 为什么不是这样?不太明白
NO.PZ2018122801000006 问题如下 In country X, the probability tha letter sent through the postsystem reaches its stination is 2/3. Assume theapostlivery is inpennt of every other postlivery, anassume thif a wife receives a letter from her husban she will certainly mail a response to her husban Suppose a man in country X mails a letter to his wife (also in country X) through the postal system. If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter? 1/3 3/5 2/3 2/5 is correct. 考点 Bayes' formul解析 (Notices: if the wife not receive the letter, she woulnot senresponse to the man.) Note: the wife receivethe letter; ¯ : the wife not receive the letter; the mreceivea response letter from his wife; ¯ : the mnot receive a response letter from his wife The question \"If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter?\" is equto figure out P( ¯ ) 考点正态分布查表 P( ¯ )= P( ¯ ) P( ¯ ) = P( ¯ )×P( ¯ | P( ¯ )×P( ¯ |A)+P( ¯ )×P( ¯ | ¯ ) 解析 题目说信可以成功寄到的概率是2/3,假设每次送信都是独立事件。同时假设妻子如果收到丈夫的信就一定会回复。问题问如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率是多少?首先丈夫没有收到回信的条件有两种情况1.丈夫的寄信丢了,就是上面那个二叉树的下面一根,概率是1/3;2.丈夫的信寄到了,但是妻子的回信寄丢了(1/3),这种情况下概率为1/3*(2/3)=2/9所以这两种情况下概率加和=1/3+2/9=5/9根据贝叶斯公式,如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率=(2/9)/(5/9)=2/5 = (2/3)×(1/3) (2/3)×(1/3)+(1/3)×1 = 2 5 妻子回信的概率应该是100%信件能否送达的概率是2/3这两个不应该相等
NO.PZ2018122801000006问题如下 In country X, the probability tha letter sent through the postsystem reaches its stination is 2/3. Assume theapostlivery is inpennt of every other postlivery, anassume thif a wife receives a letter from her husban she will certainly mail a response to her husban Suppose a man in country X mails a letter to his wife (also in country X) through the postal system. If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter? 1/3 3/5 2/3 2/5 is correct. 考点 Bayes' formul解析 (Notices: if the wife not receive the letter, she woulnot senresponse to the man.) Note: the wife receivethe letter; ¯ : the wife not receive the letter; the mreceivea response letter from his wife; ¯ : the mnot receive a response letter from his wife The question \"If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter?\" is equto figure out P( ¯ ) 考点正态分布查表 P( ¯ )= P( ¯ ) P( ¯ ) = P( ¯ )×P( ¯ | P( ¯ )×P( ¯ |A)+P( ¯ )×P( ¯ | ¯ ) 解析 题目说信可以成功寄到的概率是2/3,假设每次送信都是独立事件。同时假设妻子如果收到丈夫的信就一定会回复。问题问如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率是多少?首先丈夫没有收到回信的条件有两种情况1.丈夫的寄信丢了,就是上面那个二叉树的下面一根,概率是1/3;2.丈夫的信寄到了,但是妻子的回信寄丢了(1/3),这种情况下概率为1/3*(2/3)=2/9所以这两种情况下概率加和=1/3+2/9=5/9根据贝叶斯公式,如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率=(2/9)/(5/9)=2/5 = (2/3)×(1/3) (2/3)×(1/3)+(1/3)×1 = 2 5 老师我有两个问题第一个问题是,题目明明问的是,妻子收到丈夫的信,但丈夫没收到妻子的信,妻子只有收到丈夫的信才会回信,所以第二个树杈是不存在的。为什么不是2/3*1/3=2/9?见如下图第二个问题是左红框为什么等于右红框?课程里的贝叶斯公式只有分子的推导,没有分母的推导。
NO.PZ2018122801000006 问题如下 In country X, the probability tha letter sent through the postsystem reaches its stination is 2/3. Assume theapostlivery is inpennt of every other postlivery, anassume thif a wife receives a letter from her husban she will certainly mail a response to her husban Suppose a man in country X mails a letter to his wife (also in country X) through the postal system. If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter? 1/3 3/5 2/3 2/5 is correct. 考点 Bayes' formul解析 (Notices: if the wife not receive the letter, she woulnot senresponse to the man.) Note: the wife receivethe letter; ¯ : the wife not receive the letter; the mreceivea response letter from his wife; ¯ : the mnot receive a response letter from his wife The question \"If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter?\" is equto figure out P( ¯ ) 考点正态分布查表 P( ¯ )= P( ¯ ) P( ¯ ) = P( ¯ )×P( ¯ | P( ¯ )×P( ¯ |A)+P( ¯ )×P( ¯ | ¯ ) 解析 题目说信可以成功寄到的概率是2/3,假设每次送信都是独立事件。同时假设妻子如果收到丈夫的信就一定会回复。问题问如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率是多少?首先丈夫没有收到回信的条件有两种情况1.丈夫的寄信丢了,就是上面那个二叉树的下面一根,概率是1/3;2.丈夫的信寄到了,但是妻子的回信寄丢了(1/3),这种情况下概率为1/3*(2/3)=2/9所以这两种情况下概率加和=1/3+2/9=5/9根据贝叶斯公式,如果丈夫没有收到回信,那她的妻子收到丈夫的信的概率=(2/9)/(5/9)=2/5 = (2/3)×(1/3) (2/3)×(1/3)+(1/3)×1 = 2 5 为什么是beyes 公式,不是条件概率吗 P(A|B)
NO.PZ2018122801000006 3/5 2/3 2/5 is correct. 考点 Bayes' formula 解析 (Notices: if the wife not receive the letter, she woulnot senresponse to the man.) Note: the wife receivethe letter; A ¯ : the wife not receive the letter; the mreceivea response letter from his wife; B ¯ : the mnot receive a response letter from his wife The question \"If the mes not receive a response letter from his wife, whis the probability thhis wife receivehis letter?\" is equto figure out P(B ¯ ) P(B ¯ )= P(A B ¯ ) P( B ¯ ) = P( B ¯ )×P( B ¯ |P( B ¯ )×P( B ¯ |A)+P( B ¯ )×P( B ¯ | A ¯ ) = (2/3)×(1/3) (2/3)×(1/3)+(1/3)×1 = 2 5 这里怎么是PAB等于PB*PB|A