diff --git a/math_probability/sum_two/sum_two_challenge.ipynb b/math_probability/sum_two/sum_two_challenge.ipynb
index 2152b0f..290367c 100644
--- a/math_probability/sum_two/sum_two_challenge.ipynb
+++ b/math_probability/sum_two/sum_two_challenge.ipynb
@@ -73,7 +73,7 @@
    "source": [
     "class Solution(object):\n",
     "\n",
-    "    def sum_two(self, val):\n",
+    "    def sum_two(self, a, b):\n",
     "        # TODO: Implement me\n",
     "        pass"
    ]