NO.PZ2022123001000047
问题如下：
An analyst gathered the following information: the probability of economy prosperity is 75%, the probability of economy recession is 25%. For a company, when the economy is prosperity, there is 10% of probability that its EPS is $2.0 and 90% of probability that the EPS is $4.0. However, when the economy is recession, there is 25% of probability that the EPS is $2.0 and 75% of probability that the EPS is $4.0. What is the variance of this company’s EPS, when the economy is recession?
选项：
A.3.55
B.1.25
C.0.75
解释：
When the economy
recession:
E(EPS)
= 25% * 2 + 75% *4 = 3.5, Var(EPS) = 25% * (2-3.5)2 + 75% * (4-3.5)2
= 0.75
计算EPS的方差，用加权平均来算，为什么不能像算portfolio的方差一样权重去平方
