Question

explain this...what does that expand as....

Answer 1

That sign is called Sigma/ Summation....

As the name suggests, it means sum of the numbers...

The values written at the top and bottom of that sign show the range of values...
For eg. Here I belongs from 1 to n.....


Numerator here means sum of

f1 x1 + f2x2 + ....+ fn xn....


Similarly, Denominator means

f1 + f2 +.....+ fn.......



Hope U understand but comment if u still have some doubt