A political pollster wants to estimate the percentage of voters who will vote for the Democratic candidate in a presidential campaign. The pollster wishes to have 90% confidence that her prediction is correct to within ± 4% of the population proportion

a) What sample size is needed?
b) If the pollster wants to have 95% confidence, what sample size is needed?
c) If she wants to have a 95% confidence and a sampling error of 3%, what sample size is needed?