NO.PZ2015120604000059
问题如下：
Suppose the probability of a good economy is 0.4 and the probability of a poor economy is 0.6. The conditional probabilities of product H's profit are in the table below. What is the expected profit of product H?
选项：
A.15.
B.10.2.
C.12.5.
解释：
B is correct
E(H)=E(H|Good)+E(H|Poor)
E(H|Good) = 0.1*0+0.3*10+0.6*20=15, and E(H|Poor) = 0.5*0+0.3*10+0.2*20 = 7,
E(H) = (0.4)(15) + (0.6)(7) = 10.2.
请问这道题我虽然最后算对了但过程跟答案解析完全不同，我理解的是当H为0的时候，我是用经济好的概率0.4x0.1+0.6x0.5(经济不好时的概率）算出来加权平均为0.34，然后依次算出下面的。最后结果h为0是加权平均为0.34 为10时=0.3 为20时=0.36。
然后我再用0x0.34+10x0.3+20x0.36算出来的结果也是10.2。
