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    Statistics: Develop Confidence Interval

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    Families USA, a monthly magazine that discusses issues related to health and health
    costs, surveyed 20 of its subscribers. It found that the annual health insurance premiums
    for a family with coverage through an employer averaged $10,979. The standard deviation
    of the sample was $1,000.

    a. Based on this sample information, develop a 90 percent confidence interval for the
    population mean yearly premium.
    b. How large a sample is needed to find the population mean within $250 at 99 percent

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