# True Population

A marketing firm wants to know the proportion of Sox fans in the Chicago area within a margin of error of 8 percentage points How many people must they survey to be 99% confident that the true population proportion for the Chicago area is within this margin of error? (No prior knowledge regarding proportion is available).

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#### Solution Preview

See attachment please!

Analysis:

The general formula for a confidence interval is

estimate plus/minus (critical value )(standard deviation of the estimate )

A 99% confidence interval for proportions has the form

where N is the sample size and is the sample proportion.

If the population proportion parameter is p, the margin of error, m, for a 99% confidence interval can be calculated using the formula

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#### Solution Summary

A marketing firm wants to know the proportion of Sox fans in the Chicago area within a margin of error of 8 percentage points How many people must they survey to be 99% confident that the true population proportion for the Chicago area is within this margin of error? (No prior knowledge regarding proportion is available).