NO.PZ2020010302000008
问题如下:
What is E[XE[X]]?
Hint: recall that E[X] is a constant.
选项:
解释:
because E[X] is a constant and does not depend on X.
In other words, the expected value of a random variable does not depend on the random variable.
E[XE[X]]=ΣE[X]XPr(X=x)=E[X]ΣXPr(X=x)=E[X]∗E[X]=(E[X])2
这个公式不是很懂,E[XE[X]] 为什么等于 ΣE[X]XPr(X=x)?
谢谢