diff --git a/_psets/11.md b/_psets/11.md
index f25e4b37b965d3a95c12ac024d76babe4faea8f2..b567cd88f1c9759d015d2cd6c6f2802043a2e19a 100644
--- a/_psets/11.md
+++ b/_psets/11.md
@@ -83,7 +83,7 @@ $$
 Plugging in the values above we find
 
 $$
-2mgv = -h i n^2 f^2
+4mgv = -h i n^2 f^2
 $$