Question

1.已知随机变量X的概率分布列如下所示,则他的方差是

Answer 1

--------------1.-------------

E(x)=1*0.4+3*0.1+5*0.5

=0.4+0.3+2.5

=3.2

D(x)=1^2*0.4+3^2*0.1+5^2*0.5-3.2^2

=0.4+0.9+12.5-10.24

=3.56

--------------2.-------------

(C(3,2)+C(3,1))*2*2

=(3+3)*2*2

=24