diff --git a/ml2/3_3_Data_Munging_with_Pandas.ipynb b/ml2/3_3_Data_Munging_with_Pandas.ipynb
index 5467e85..1ecd01d 100644
--- a/ml2/3_3_Data_Munging_with_Pandas.ipynb
+++ b/ml2/3_3_Data_Munging_with_Pandas.ipynb
@@ -373,8 +373,8 @@
    "source": [
     "#Mean age of  passengers per Passenger class\n",
     "\n",
-    "#First we calculate the mean\n",
-    "df.groupby('Pclass').mean()"
+    "#First we calculate the mean for the numeric columns\n",
+    "df.select_dtypes(np.number).groupby('Pclass').mean()"
    ]
   },
   {