Political Science, Inc. (PSI) specializes in voter polls and surveys designed to keep political office seekers informed of their position in a race. Using telephone surveys, interviewers ask registered voters who they would vote for if the election were held that day.In a recent election campaign, PSI found that 220 registered voters, out of 500 contacted, favored a particular candidate.
a. PSI wants to develop a 95% confidence interval estimate for the proportion of the population of registered voters that favors the candidate.
b. Suppose that PSI would like 99% confidence that the sample proportion is within +/- .03 of the population proportion. How large a sample size is needed to provide the desired margin of error?

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The Answer of Political Science, Inc. (PSI) specializes in voter polls and surveys designed to keep political office seekers informed of their position in a race. Using telephone surveys, interviewers ask registered voters who they would vote for if the election were held that day.In a recent election campaign, PSI found that 220 registered voters, out of 500 contacted, favored a particular candidate.
a. PSI wants to develop a 95% confidence interval estimate for the proportion of the population of registered voters that favors the candidate.
b. Suppose that PSI would like 99% confidence that the sample proportion is within +/- .03 of the population proportion. How large a sample size is needed to provide the desired margin of error?