A Local Health Center Noted That in a Sample of 400

Short Answer

A local health center noted that in a sample of 400 patients 80 were referred to them by the local hospital.
a.Provide a 95% confidence interval for all the patients who are referred to the health center by the hospital.
b.What size sample would be required to estimate the proportion of hospital referrals with a margin of error of 0.04 or less at 95% confidence?