Question

若掷一颗骰子的点数为X,则D(X)等于

Answer 1

求D（X）,就是求方差

掷骰子可能得到的数字为1,2,3,4,5,6

平均值为3.5

D(X)=1/6*[(1-3.5)^2+(2-3.5)^2+(3-3.5)^2+(4-3.5)^2+(5-3.5)^2+(6-3.5)^2]

=35/12

选B