Another important concept in probability theory that we will use a lot is expected value, the mean, or average-- those are all roughly interchangeable concepts.

概率论中另外一个常用的重要的概念是,期望值或者也叫均值,这两个概念可以互换

耶鲁公开课 - 金融市场课程节选

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

耶鲁公开课 - 金融市场课程节选