diff --git a/slides.md b/slides.md
index 639ccfb..59db188 100644
--- a/slides.md
+++ b/slides.md
@@ -33,3 +33,7 @@ import this
 for i in range(10):
     print("Hello world")
 ```
+
+# Some math
+
+$$\bar{x}_w = \frac{\sum_{i=1}^n w_i x_i}{\sum_{i=1}^n w_i} $$