Starting with the 75 estimate for Italians how large a sampl

Starting with the 75% estimate for Italians, how large a sample must you collect in order to estimate the proportion of PTC tasters within

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*0.75*(1-0.75)

=140.9388

Take n=141