The medical director of Mercy Hospital has asked a staff analyst to develop a 98% confidence interval estimate of the time required for a certain type of heart surgery. She would like to be accurate within + or - 6 min. Only 420 such operations have been performed nationwide. For the eight operations performed in the region of Mercy Hospital, X bar= 3.20 hr. and s = .30 hr. The analyst plans to take a random sample.
How large a sample should be?
n=(zs)/E^2=(2.33*0.3/0.1)^2 = 48.86 or 49 where E = 6 minutes or 6/60 = 0.1 hr.