If cinderella clothes, inc. has determined that 0.5% of all incoming phone calls involve complaints, what is the probability that in 200 incoming calls there are more than one complaint? --


This is a binomial distribution problem.

Number of trials n=200,
probabiltiy of success p=.5%=.005.

Let X be the random variable than counts the number of complains. In the problem we need to find

P{X > 1}= 1- P{X=0} - P{X=1}.

No Complaint: P{X=0} (1-p)n= (1-.005)200 = .3670 and

One complaint: P{X=1} = 200*p*(1-p)n-1 = 200*(.005)*(1-.005)199 = .3688
So, P{X>1}= 1- .3670 -3688 =.2642

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