That's called the expected value. People also call that the mean or the average.

这叫做期望值，人们也成为均值或平均值。

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And you can take pleasure in knowing that, according to the U. S. Forest Service, trees call boost the market value of your home by an average six or seven percent.

而且，根据美国林业服务部门的说法，树木能使你房产的市场价值提升平均六到七个百分点，你一定很高兴了解到这一点。

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