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Thread: 99% confidence interval

  1. #1
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    99% confidence interval




    I have worked on this problem for awhile trying it different ways -

    A random sample of 250 students at a university finds that these students take a mean of 15 credit
    hours per quarter with a standard deviation of 1.6 credit hours. Estimate the mean credit hours
    taken by a student each quarter using a 99% confidence interval.
    Mean: 15
    Standard deviation σ: 1.6 # of Samples : 250 Confidence interval %: 99%
    Standard deviation σx of the set of sample mean = σ / √n
    σx = 0.101

    99% of the sample means should be within 2.576 standard deviations of the population mean.
    Therefore,
    Confidence interval = Sample Mean 2.576 σx
    = 15 2.576 0.101
    = 15 0.261

    I had other choices such as 15 + - .013; 15 + - .016 and 15 + - 206 but with my calculations I ended up with my solution of 15 + - 0.261


    Does anyone think I did this correctly or did I make a mistake somewhere...

    Statistics is a bit challenging for me and any input would be greatly appreciated.

    Thanks and have a great holiday.

  2. #2
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    Your answer is correct. The given solutions are wrong. Well done! :-)

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