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Thread: Hey guys just looking for help with this question dealing with population variance.

  1. #1
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    Hey guys just looking for help with this question dealing with population variance.

    I don't quite know how to write this problem down here, so I'll just do it in paint and post up a link.

    imgur: the simple image sharer

    Thanks, it would be helpful if you could explain it to me through paint also, as I don't really understand math displayed on a computer. I just don't know how to proceed on the question, and i don't even know what exactly it is asking me to do.
    Last edited by Joyeux; Mar 15th 2013 at 08:09 PM.
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  2. #2
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    Re: Hey guys just looking for help with this question dealing with population varianc

    Quote Originally Posted by Joyeux View Post
    I don't quite know how to write this problem down here, so I'll just do it in paint and post up a link.

    imgur: the simple image sharer

    Thanks, it would be helpful if you could explain it to me through paint also, as I don't really understand math displayed on a computer. I just don't know how to proceed on the question, and i don't even know what exactly it is asking me to do.
    Your equality is not true. The mean $\displaystyle \mu$ is missing an exponent of 2. See below (by the way, this is "math displayed on a computer", and I'm not quite sure how this is worse than "numbers by paint"):

    $\displaystyle \sigma^2=\sum_{i=1}^n \frac{(x_i-\mu)^2}{n} = \sum_{i=1}^n \frac{x_i^2}{n} - 2\sum_{i=1}^n \frac{x_i \mu}{n} + \sum_{i=1}^n \frac{\mu^2}{n} $
    $\displaystyle = \sum_{i=1}^n \frac{x_i^2}{n} - 2\mu\left(\sum_{i=1}^n \frac{x_i}{n}\right) + n\frac{\mu^2}{n}$
    $\displaystyle = \sum_{i=1}^n \frac{x_i^2}{n} - 2\mu^2 + \mu^2$
    $\displaystyle = \sum_{i=1}^n \frac{x_i^2}{n} - \mu^2$
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  3. #3
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    Re: Hey guys just looking for help with this question dealing with population varianc

    Oops sorry I edited it, I still don't know how to solve it though. I don't think it's asking to change from one form to another. Your solution didn't have the substituted version of mu. Still really confused.
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  4. #4
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    Re: Hey guys just looking for help with this question dealing with population varianc

    I think this is the question it's asking, imgur: the simple image sharer. Still not 100% sure though.
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