概率题求出数学期望后怎么求方差

Question

如题所述

Answer 1

随机变量：X {x1，x2+，. . . ，+xn}
数学期望：EX = (x1+x2+ . . . +xn)/n
方差：VAR = E{(x-EX)²}
举例：X {1,2,3,4,5}
EX=3
VAR =[(1-3)²+(2-3)²+0²+1²+2²]/5 = 10/5 = 2