diff --git a/education/statistics/Hypothesis Tests.md b/education/statistics/Hypothesis Tests.md
index ac6995b..5ea00f8 100644
--- a/education/statistics/Hypothesis Tests.md	
+++ b/education/statistics/Hypothesis Tests.md	
@@ -70,6 +70,8 @@ Reliable investigators test their conclusions on an independent batch of data
 ## Goodness of fit tests ($\chi ^2$) 
 This test is used when you have one qualitative variable with many categories, eg the (color, size, shape) of an (item).
 
+$$ \chi ^2 = sum(\frac{(obs_{freq} - exp_{freq})^2}{exp_{freq}}) $$
+
 The $\chi^2$ curve does not follow the normal curve. It has a long right hand tail. As the degrees of freedom go up, the curves flatten out, and the hump moves out to the right. 
 
 $$ df = num_{terms} - 1 $$