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    confidence intervals




    I have a question that is driving me up the wall.

    A sample of size 400 has a (sum)x = 30,430 and (sum)xsquared = 3,261,1000.
    construct a 95% confidence interval for the approriate mean (mew).

    I got the t-score to be 1.966 and the x avaerage to be 76.075 but when trying to do the confidence interval I don't know what to put in for s becuase i don't know how to find s (part of the studentized version) s is equal to standard deviation. does anyone know how to find this?

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    There is a computational formula for the standard deviation that uses the sum of x and the sum of x^2.



    Sx = Square root of {Ex2 - [(Ex)2]/n}/n-1

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    caluculations

    so with those numbers I would get SX equal to 8172.80 if i did it correctly?

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    I made a correction - the summation symbols didn't go in correctly.

    You should get Sx = 48.7

    Ex = 30,430
    Ex^2 = 3,261,100
    (Ex)^2 = 925,984,900

    Sx = Square root of {Ex2 - [(Ex)2]/n}/n-1

    = sqrt [ (3261100 - (925,984,900/400)) / 399 ]

    = sqrt (946137.75 / 399)
    = sqrt (2371.27)
    = 48.7

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    yay


    thanks for the help!

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