NO.PZ2015120604000063
问题如下:
According to the above table, what is the covariance of X and Y?
选项:
A.0.72.
B.-4.8.
C.-0.72.
解释:
B is correct
Cov(X,Y) = 0.2(-2-1)(5-1.6) + 0.6(1-1)(2-1.6) +0.2(4-1) (-3-1.6) = -4.8
Y均值=0.2*5+0.6*2+0.2*(-3)=1.6
公式里1怎么算出来的