设XB(n,p),求D(X)/E(X)=?

Question

设 X B(n,p),求 D(X)/E(X)=?

Answer 1

E(X)=Ex1+Ex2+……+Exn=np
D(X)=E(X2)-(EX)2 (这里的2指平方啊.)
=np（1-p）
D(X)/E(X)=1-p