Hello from saudi arabia
Welcome to Math Help Forum! 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 : I need to the proof ... The formula for the mean is:$\displaystyle \bar{x}=\frac{\sum_{i=1}^nf_ix_i}{\sum_{i=1}^nf_i}$
$\displaystyle \Rightarrow\bar{x}\sum_{i=1}^nf_i=\sum_{i=1}^nf_ix _i$
$\displaystyle 0=\Rightarrow\sum_{i=1}^nf_ix_i-\sum_{i=1}^nf_i\bar{x}$
$\displaystyle \Rightarrow\sum_{i=1}^nf_i(x_i-\bar{x})=0$
Grandad