# Deriving Chi-Square for contingency table 2x2

#### newbiekakak

##### New Member
Hi
Given a 2x2 contingency table, with a b c d as the observed values and n as the total, I have to show from the fact that Chi-Square = Sum(((O-E)^2)/E) Where E is the expected value of the observed, that:
I just cant seem to get there. Any links or tips about how this formula is derived?