mitmit · 2021年07月14日
NO.PZ2015120604000076
问题如下：
According to the above table, and we are informed that the performance of next day is good, what is the probability of today's performance is good?
选项：
A. 0.74.
B. 0.28.
C. 0.67.
解释：
C is correct.
We can use Bayes' formula to solve this problem.
A: today's performance is good.
B: next day's performance is good.
答案的所有的可能性也没看懂，题目没说在所有可能性下求这两天都好的概率吧.
Olive_品职助教 · 2021年07月15日
嗨，从没放弃的小努力你好：
这道题问，在下一天是good的情况下，today是good的概率，也就是答案里写的P（A丨B）。
答案直接带入贝叶斯公式：
我们知道P（B丨A）=0.7，这是从表格里能找到的。
P（A）=0.4，这也是表格已知数据。
P（B）是next day是good的概率，next day是good的概率就是0.4×0.7+0.2×0.3+0.4×0.2。
题目只是已知了next day是good，我们并不知道是从哪个路径过去的，第一天是good、neural、poor这三种情况都可能有第二天是good的情况。所以当然要都考虑。
----------------------------------------------加油吧，让我们一起遇见更好的自己！
NO.PZ2015120604000076问题如下 Accorng to the above table, anwe are informeththe performanof next y is goo whis the probability of toy's performanis goo A.0.74.B.0.28.C.0.67. C is correct.We cuse Bayes' formula to solve this problem.toy's performanis goonext y's performanis gooP(A|B)=P(B|A)*P(A)/P(B)=0.7×0.4/(0.4×0.7+0.2×0.3+0.4×0.2)P(B|A)*P(A)=0.7×0.4=0.28P(B)=0.4×0.7+0.2×0.3+0.4×0.2=0.42P(A|B)=0.67 我的理解贝叶斯公式是P（A｜B）=P（B｜A）*P（A）/P（B），P（B｜A）=0.4*0.7，P（B）=0.4*0.7+0.2*0.3+0.4*0.2=0.42，P（A）=0.4，但是这样算下来跟答案不一样，是不是P（A）错了？
NO.PZ2015120604000076 问题如下 Accorng to the above table, anwe are informeththe performanof next y is goo whis the probability of toy's performanis goo A.0.74. B.0.28. C.0.67. C is correct.We cuse Bayes' formula to solve this problem.toy's performanis goonext y's performanis gooP(A|B)=P(B|A)*P(A)/P(B)=0.7×0.4/(0.4×0.7+0.2×0.3+0.4×0.2)P(B|A)*P(A)=0.7×0.4=0.28P(B)=0.4×0.7+0.2×0.3+0.4×0.2=0.42P(A|B)=0.67 这个题目有问题吧？题目的意图是想考察条件概率，但是问法并不是，问的就是一个独立事件的概率。
NO.PZ2015120604000076 问题如下 Accorng to the above table, anwe are informeththe performanof next y is goo whis the probability of toy's performanis goo A.0.74. B.0.28. C.0.67. C is correct.We cuse Bayes' formula to solve this problem.toy's performanis goonext y's performanis gooP(A|B)=P(B|A)*P(A)/P(B)=0.7×0.4/(0.4×0.7+0.2×0.3+0.4×0.2)P(B|A)*P(A)=0.7×0.4=0.28P(B)=0.4×0.7+0.2×0.3+0.4×0.2=0.42P(A|B)=0.67 这个题用贝叶斯公式怎么画图啊
NO.PZ2015120604000076 问题如下 Accorng to the above table, anwe are informeththe performanof next y is goo whis the probability of toy's performanis goo A.0.74. B.0.28. C.0.67. C is correct.We cuse Bayes' formula to solve this problem.toy's performanis goonext y's performanis gooP(A|B)=P(B|A)*P(A)/P(B)=0.7×0.4/(0.4×0.7+0.2×0.3+0.4×0.2)P(B|A)*P(A)=0.7×0.4=0.28P(B)=0.4×0.7+0.2×0.3+0.4×0.2=0.42P(A|B)=0.67 如题
NO.PZ2015120604000076 问题如下 Accorng to the above table, anwe are informeththe performanof next y is goo whis the probability of toy's performanis goo A.0.74. B.0.28. C.0.67. C is correct.We cuse Bayes' formula to solve this problem.toy's performanis goonext y's performanis gooP(A|B)=P(B|A)*P(A)/P(B)=0.7×0.4/(0.4×0.7+0.2×0.3+0.4×0.2)P(B|A)*P(A)=0.7×0.4=0.28P(B)=0.4×0.7+0.2×0.3+0.4×0.2=0.42P(A|B)=0.67 老师，这个式子完全没看懂，麻烦一下每一步。谢谢
