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    Sample size for estimating a population mean

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    A consumer advocacy group is doing a large study on car rental practices. Among other things, the consumer group would like to estimate the mean monthly mileage,µ , of cars rented in the U.S. over the past year. The consumer group plans to choose a random sample of monthly U.S. rental car mileages and then estimate µ using the mean of the sample.

    Using the value 800 miles per month as the standard deviation of monthly U.S. rental car mileages from the past year, what is the minimum sample size needed in order for the consumer group to be 99% confident that its estimate is within 175 miles per month of µ ?

    Carry your intermediate computations to at least three decimal places. Write your answer as a whole number (and make sure that it is the minimum whole number that satisfies the requirements).

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    Solution Summary

    This solution shows how to determine the sample size necessary to construct a confidence interval for a population mean when the margin of error must be within a given amount and the interval must have a given level of confidence.