设X~B(n,p),且E(X)=12,D(X)=4,则n与p的值分别为()
A.18,
B.12,
C.18,
D.12,
罗永春回答:
∵随机变量X服从二项分布X~B(n,p),且E(X)=12,D(X)=4,
∴E(X)=12=np,①
D(X)=4=np(1-p),②
①与②相除可得1-p=
设X~B(n,p),且E(X)=12,D(X)=4,则n与p的值分别为()
A.18,
B.12,
C.18,
D.12,
罗永春回答:
∵随机变量X服从二项分布X~B(n,p),且E(X)=12,D(X)=4,
∴E(X)=12=np,①
D(X)=4=np(1-p),②
①与②相除可得1-p=