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Math Help - Trouble calculating a confidence interval

  1. #1
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    Trouble calculating a confidence interval

    Your company plans to buy disks that are supposed to come in containers of exactly 100 disks. A random sample of 49 containers is taken and the mean is found to be 102 disks with a standard deviation of 3 disks.
    (a) Using a .05 significance level, should the disk -packing machinery be adjusted?
    (b) Construct a two-sided 95% confidence interval about the mean using the above data.
    Last edited by mr fantastic; April 15th 2009 at 01:04 AM. Reason: Moved from another thread
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  2. #2
    Senior Member Twig's Avatar
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    hi

    hi

     \left[\mu^{*} -\lambda_{0.05} \cdot \sigma^{*} , \mu^{*} +\lambda_{0.05} \cdot \sigma^{*} \right] - Asymptotic normality

    where  \mu^{*} \mbox{ is the estimated mean, and } \sigma^{*} is the estimated standard deviation.

    If the number of observations n is not large enough, use

    \left[ \mu^{*} -t_{\frac{\alpha}{2}}(n-1) \frac{s_{n-1}}{\sqrt{n}}, \mu^{*} +t_{\frac{\alpha}{2}}(n-1) \frac{s_{n-1}}{\sqrt{n}} \right]

    The later is the so-called Students t-distribution, with  f=n-1
    degrees of freedom. For this you need the t-distribution table.
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