Question

A political candidate has asked you to conduct a poll to determine what percentage of people support her. If the candidate only wants a 7% margin of error at a 99% confidence level, what size of sample is needed?

Answer 1

Here Margin of Error is E=0.07

z value for 99% CI is 2.576 as P(-2.576<z<2.576)=0.99

So we will find n using formula of E

$E=z*\sqrt{\frac{pq}{n}}$

So

E b*d*20) = n = n

As p is not given we will take p=0.5

$n=(\frac{z}{E})^2*p*q=(\frac{2.576}{0.07})^2*0.5*0.5=338.56=339$