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Math Help - 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; March 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 \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"):

    \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}
     = \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}
     = \sum_{i=1}^n \frac{x_i^2}{n} - 2\mu^2 + \mu^2
     = \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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