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Math Help - Not Sure how to even start this one

  1. #1
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    Not Sure how to even start this one

    The mean number of travel days per year for salespeople employed by hardware distributors needs to be estimated with a 98% degree of confidence. For a small pilot study the mean was 150 days and the standard deviation was 12 days. If the population mean is estimated within four days, how many salespeople should be sampled?
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  2. #2
    Senior Member MaxJasper's Avatar
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    Lightbulb Re: Not Sure how to even start this one

    m=150
    s=12 =sample sd
    \sigma =s\sqrt{n} = population sd
    z_{.98}=2.3263 two-sided normal distribution z-value

    -\sigma  z_{.98}\leq m\pm 4\leq \sigma  z_{.98}

    m+4\leq s z_{.98}\sqrt{n}

    Solve to obtain:

    n > 30
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