随机变量，如上例中的时间，与一些特性相关，这些特性不同于那些与单个值相关的特性。
A random variable, such as time in the example above, is associated with properties that are different from those associated with a single value.
在数学术语中，不完全确定的值称为随机变量。
In mathematical terms, values that are not known with complete certainty are called random variables.
随机变量的方差衡量随机变量值与期望值偏离的程度。
The variance of a random variable measures how far from the expected value its values typically are.
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