But they're accountable and we can list all possible values when they're discrete and form a probability weighted average of the outcomes.

但随机变量是离散的话,我们可以把所有的可能值列出来,然后算出加权平均值

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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

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