问题如下图：
选项：
A. 
B. 
C. 
解释：
不应该是0.4*0.2吗？
星星_品职助教 · 2019年09月03日
同学你好，
对于本题而言，考察的并不是计算，而是条件概率conditional probability的定义。条件概率指得是在A事件已经发生的“条件”下，B事件再发生的概率，也就是P(B|A)。
以本题为例，如果假设事件A代表今天市场的情况；事件B代表明天市场的情况。表格的最后一列直接就是P(B|A)，拿来直接用就可以。
例如B选项，解析一下就是在今天市场表现为poor的条件下，明天市场情况是good的条件概率是多少，所以直接从最后一行（代表今天市场为poor）的最后一列中找到good对应的条件概率也就是0.2即可。A和C选项也这么分析。
而下一题也就是PZ2015120604000074涉及到你说的计算，也就是如何通过已知的条件概率去求联合概率，可以把这两道题对比来看，有助于理解概念。
概率这个地方很容易混淆，建议把握好每个基础概念，然后多看几遍。加油
NO.PZ2015120604000073 问题如下 Accorng to the above table, whiof the following statements is the most correct? A.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.01. B.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.20. C.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.50. B is correct.P(gooperformanof next y/poor performanof toy)=0.2, whiis shown in the table. 04*0.2除以（0.4*0.2+0.4*0.5+0.4*0.3）
NO.PZ2015120604000073 问题如下 Accorng to the above table, whiof the following statements is the most correct? A.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.01. B.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.20. C.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.50. B is correct.P(gooperformanof next y/poor performanof toy)=0.2, whiis shown in the table. 这道题不是说在一个事件发生的前提下，这个事件发生吗？不应该用P(B|A)=P(AB)/P(A)这个公式吗？就是0.2/0.4
NO.PZ2015120604000073 问题如下 Accorng to the above table, whiof the following statements is the most correct? A.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.01. B.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.20. C.If performanof toy's bonmarket is poor, the contionprobability of having gooperformanof next y's bonmarket is equto 0.50. B is correct.P(gooperformanof next y/poor performanof toy)=0.2, whiis shown in the table. （1）请问老师，这段题目如何判断出表达的是条件概率，而不是二叉树（需要相乘）~（2）如果题目答案为相乘形式，即第一天市场poor的概率乘以第二天市场goo概率，请问题干一般如何表达？谢谢老师。
老师可以写一下具体计算过程吗？