Question

If np >5 and nq>5 estimate P (fewer than 4) with n=13 p=0.4 by using normal distribution as an approximate to the binomial distribution if np <5 or nq< then state that the normal approximation is not suitable.

Answer 1

The Normal approximation to the binomial 

is as follows

mean=13(.5)=6.5 
variance=6.5(.5)=3.25 
Pr[fewer than 4]= 
Pr[N<=3] Apply the continuity correction 
Pr[N<=3.5]~=Pr[Z<3.5-6.5/sqrt(3.25)]= 

Pr[Z<-1.66]=0.048457226

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