The variance of a random variable measures how far from the expected value its values typically are.

随机变量的方差衡量随机变量值与期望值偏离的程度。

youdao

The basic definition-- the expected value of some random variable x--E--I guess I should have said that a random variable is a quantity that takes on value.

最基本的定义,某一个随机变量X的期望值E,我应该提到过,随机变量是一个可以取值的数

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