find the sample size n needed to find the estimate the perc

find the sample size n , needed to find the estimate the percentage of adults who have consulted fortune tellers . USes 0.04 margin error use a confidence level of 98% and usng results from a prior poll suggesting that 20% adults have consulted fortune tellers. N=___

Solution

Given a=1-0.98=0.02, Z(0.02/2)=Z(0.01) =2.33 (from standard normal table)

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

=(2.33/0.04)^2*0.2*0.8

=542.89

Take n=543