diff --git a/docs/mhf4u7.md b/docs/mhf4u7.md
index 4ecee2d..653e9fe 100644
--- a/docs/mhf4u7.md
+++ b/docs/mhf4u7.md
@@ -54,7 +54,7 @@ A **frequency distribution** is a table that lists categories/ranges and the num
 A frequency distribution table includes:
 
  - A number of classes, all of the same width.
-	- This number is arbitrarily chosen, but a commonly used formula is $\lceil\sqrt{\text{# of elements}}\rceil$.
+	- This number is arbitrarily chosen, but a commonly used formula is $\lceil1+3.3\log({\text{# of elements})}\rceil$.
 	- The width (size) of each class is $\lceil\frac{\text{max} - \text{min}}{\text{# of classes}}\rceil$.
 	- Each class includes its lower bound and excludes its upper bound ($\text{lower} ≤ x < \text{upper}$)
 	- The **relative frequency** of a data set is the percentage of the whole data set present in that class in decimal form.