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Math Help - Questions about Confidence Interval

  1. #1
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    Arrow Questions about Confidence Interval

    Hi,
    I could not find the answer of these two questions, can anyone help me ?
    thanks in advance.

    1- A tool manufacturer’s choose randomly 10 pieces from a batch. The measured weights are listed below. Supposing the distribution as normal, please calculate 99% CI of the population variance.
    (51, 50, 60, 53, 59, 54, 56, 51, 59, 58)


    2- 450 pieces of a machine tool have been produced with a variance of 300 grams2 . Please find for variance the CI of 95%. (solve the problem as a large sample)
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  2. #2
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    hello
    for 1:
    first find the variance and the average of the numbers,name them s,u then use this equation?:

    T=(Xn-u)/(s/sqrt(n)) ~ t(n-1)
    a=.99 -> 1-a=.01
    p(-Ta/2<T<Ta/2) =p(-T.05<T<T.05) find this from the table of the t distribution.
    for 2 is also as above
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  3. #3
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    Smile

    Dude,thanks a lot
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  4. #4
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    Quote Originally Posted by neilbuster View Post
    Hi,
    I could not find the answer of these two questions, can anyone help me ?
    thanks in advance.

    1- A tool manufacturer’s choose randomly 10 pieces from a batch. The measured weights are listed below. Supposing the distribution as normal, please calculate 99% CI of the population variance.
    (51, 50, 60, 53, 59, 54, 56, 51, 59, 58)


    2- 450 pieces of a machine tool have been produced with a variance of 300 grams2 . Please find for variance the CI of 95%. (solve the problem as a large sample)
    Read this: Estimating the Variance

    Quote Originally Posted by abdolah View Post
    hello
    for 1:
    first find the variance and the average of the numbers,name them s,u then use this equation?:

    T=(Xn-u)/(s/sqrt(n)) ~ t(n-1)
    a=.99 -> 1-a=.01
    p(-Ta/2<T<Ta/2) =p(-T.05<T<T.05) find this from the table of the t distribution.
    for 2 is also as above
    You have misread the question. Confidence interval for the variance (NOT the mean) is required.
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