Replace method for the one in the instructions

Mission610Solutions.ipynb

@@ -436,7 +436,7 @@
     }
    ],
    "source": [
-    "countries_frequency = df.groupby(\"Country\").count()\n",
+    "countries_frequency = df.groupby(\"Country\").value_counts()\n",
     "print_pretty_table(countries_frequency)"
    ]
   },