Determine the sample size n needed to construct a 90 confide

Determine the sample size n needed to construct a 90% confidence interval to estimate the population proportion when p=0.38 and the marin of error equals 6%.

n = ?

Solution

Given a=1-0.9=0.1, Z(0.05) = 1.645 (from standard normal table)

So n=(Z/E)^2*p*(1-p)

=(1.645/0.06)^2*0.38*(1-0.38)

=177.0943

Take n=178