# new member need to help

• November 30th 2009, 08:54 AM
from saudi arabia
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 :

http://www14.0zz0.com/2009/11/30/17/304447025.gif
I need to the proof ...
• November 30th 2009, 10:04 AM
Hello from saudi arabia

Welcome to Math Help Forum!
Quote:

Originally Posted by from saudi arabia
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 :

http://www14.0zz0.com/2009/11/30/17/304447025.gif
I need to the proof ...

The formula for the mean is:
$\bar{x}=\frac{\sum_{i=1}^nf_ix_i}{\sum_{i=1}^nf_i}$

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

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

$\Rightarrow\sum_{i=1}^nf_i(x_i-\bar{x})=0$