Processing math: 100%


1)

Let XB(n,p),ifE(x)=5,Var(X)=2.5,   then p(X<1) is equal to 


A) (12)11

B) (12)10

C) (12)8

D) (12)9

Answer:

Option B

Explanation:

Given  , mean E(X)=5, and variance , Var(X)=2.5

    np=5 and npq=2.5

  5q=2.5 q=12

    p+q=1

     p=112=12

np=5                  

  n×12=5                 [p=12]

     n=10

p(X<1)=p(X=0)=nCrprqnr

= p(X<1)=p(X=0)=10C0(12)0(12)100

=1×1×(12)10=(12)10