期望和方差设随机变量X具有分布律P(X=i)=0.2,i=1,2
设随机变量X具有分布律 P(X= i)=0.2, i=1,2,3,4,5 求E(X) ,D(X)
期望E(X)=1*0.2+2*0.2+...+5*0.2=15*0.2=3. 方差D(X)=[(1-3)^2+(2-3)^2+(3-3)^2+(4-3)^2+(5-3)^2]*0.2 =[4+1+0+1+4]*0.2=2.