设离散型随机变量 ξ的概率分布为Ｐ(ξ =ｘｉ) =ｐｉ,ｉ =1 ,2 ,3,… ,则Ｅξ =ｘ1ｐ2+ｘ2 ｐ2 +ｘ3ｐ3+…叫做随机变量 ξ的数学期望 (简称期望 ) .数学期望是随机变量的一个重要数学特征 ,它代表了随机变量总体取值的平均水平 .下面举例谈谈数学期望在效益、利润等经济问题? Let the probability distribution of the discrete random variable ξ be P(ξ = xi) = pi,i =1,2,3,..., then Eξ =x1p2+x2 p2 +x3p3+... is the mathematical expectation of the random variable ( (abbreviated as expectation) Mathematical expectation is an important mathematical feature of a random variable, which represents the average level of the random variable’s overall value. Here is an example to talk about mathematical expectations in the economic problems such as efficiency, profit, etc.?