Question

若随机变量X1-B(n,0.2),X2-B(6,p),X3-B(n,p),且E（X1）=2,D(X2)=3/2.则D(X

Answer 1

E（X1）=np=0.2n=2,=> n=10

D(X2)=3/2=6p(1-p) 4p²-4p+1=0 =﹥p=0.5

X3-B(n,p)=B(10,0.5),D(X3)=10*0.5*0.5=2.5