Please will somebody explain to me how to do this?

Question

A factory makes silicon chips for use in computers. It is known that about 90% of
the chips meet specifications. Every hour a sample of 18 chips is selected at random for testing and the number of chips that meet specifications is recorded. What is the
approximate mean and standard deviation of the number of chips meeting
specifications?

Answer 1

Since 90% meet specifications we can say p=.9 .

 

Also, since we are sample from a large population we can assume the distribution is essentially binomial in the case with n=18 and p=.9 (and therefore q=.1).

 

Using the formulas mean=np  and s.d.= sqroot(npq) substitute n,p,q in the formulas to calculate.

 

 

Do you have any questions or need more explanation?