Statistics

What?

if x=5

5-5=0 :P

You mean there are a set X, 

(sum of all terms of set X) - (number of terms in X) =0?

This equation is only possible when all the terms in set X is 1.

X = (1, 1, 1, 1, 1, 1, 1, 1, 1) <--- This is one set that satisfies the equation.