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叶赫那拉坤坤 · 2020年02月08日

问一道题:NO.PZ2015120604000062

问题如下:

According to the above table, what is the variance of X?

选项:

A.

3.6.

B.

1.90.

C.

6.64.

解释:

A is correct

Firstly ,We calulate expected return of X, E(X) = (0.2)(-2) + (0.6)(1) + (0.2)(4) = 1,

Then,Var(X) = 0.2(-2-1)2 + 0.6(1-1)2 + 0.2(4-1)2 = 3.6

这个题与y有什么关系呀?

第一步的期望不知道怎么算


1 个答案

星星_品职助教 · 2020年02月08日

同学你好,

这个是联合概率矩阵,这个矩阵在covariance那个知识点的例子里是有讲的,可以复习一下

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