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Math Help - new member need to help

  1. #1
    Newbie
    Joined
    Nov 2009
    From
    saudi arabia
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    Exclamation new member need to help

    I very happy to register in this forum ...

    and I need to some help to find this proof ..

    from the properties of arithmetic mean for grouped data :


    I need to the proof ...
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  2. #2
    MHF Contributor
    Grandad's Avatar
    Joined
    Dec 2008
    From
    South Coast of England
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    2,570
    Hello from saudi arabia

    Welcome to Math Help Forum!
    Quote Originally Posted by from saudi arabia View Post
    I very happy to register in this forum ...

    and I need to some help to find this proof ..

    from the properties of arithmetic mean for grouped data :


    I need to the proof ...
    The formula for the mean is:
    \bar{x}=\frac{\sum_{i=1}^nf_ix_i}{\sum_{i=1}^nf_i}

    \Rightarrow\bar{x}\sum_{i=1}^nf_i=\sum_{i=1}^nf_ix  _i

    0=\Rightarrow\sum_{i=1}^nf_ix_i-\sum_{i=1}^nf_i\bar{x}

    \Rightarrow\sum_{i=1}^nf_i(x_i-\bar{x})=0
    Grandad
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  3. #3
    Newbie
    Joined
    Nov 2009
    From
    saudi arabia
    Posts
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    I very thank Mr Grandad to help me..

    because I have three days to search in arabic sites .. and I have statistic exam ..
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