问题如下:
According to the above probability matrix, the covariance of stock A and stock B is:
选项:
A.-0.165.
B.-0.0657.
C.0.009.
D.-0.0567.
解释:
B is correct.
考点:Covariance & Correlation Coefficient
解析:协方差的公式为COV(A,B)=E(AB)-E(A)E(B)
E(AB)=0.3*(-20%)*70%+0.4*20%*30%+0.3*30%*(-20%)=-0.042+0.024-0.018=-0.036
E(A)=(-20%)*0.3+20%*0.4+30%*0.3=-0.06+0.08+0.09=0.11
E(B)=70%*0.3+30%*0.4-20%*0.3=0.21+0.12-0.06=0.27
所以COV(A,B)=E(AB)-E(A)E(B)=-0.036-0.11*0.27=-0.0657
你好,请教几个问题:
①E(AB)的算法是讲义哪部分的知识点。
②E(A)和E(B)的算法就是取值乘以相应概率吗。