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Math Help - Unbiased sample variance question

  1. #1
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    Apr 2011
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    Unbiased sample variance question

    I have what should be a very simple problem, however I'm sure the answer im getting is wrong =(

    Calculate the unbiased sample variance of the following numbers (weights of bags of sugar, not that it makes a difference).

    1013, 997, 1013, 1013, 1004, 985, 991, 997

    I know the formula is

    ( 1 / (n-1) ) * Sum((xi-mean)^2)

    So i plug in the numbers, and i get

    mean = 1001.625

    For Sum((xi-mean)^2) I get 825.875 (wrong?)

    Then plugging in the values I end up with a variance of 117.98 which is clearly wrong, I think it should be 10.86ish.

    Can anyone point out my (probably trivial) error please?

    Thanks in advance.
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  2. #2
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    Apr 2011
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    *smacks head into desk repeatedly*

    What a moron I am, all I needed to do was sqrt my answer...............

    I've been awake too long.. Thats my excuse..

    How the hell do I delete this thread before you all realise i'm a moron?
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