diff --git a/04_measuring_quality_of_a_classifier.ipynb b/04_measuring_quality_of_a_classifier.ipynb
index 913a4dd952b9e8c8ed8bd5738c1113f00432e5d6..914bf43af56b532ae8c4a1dfa618a3ec64a45f81 100644
--- a/04_measuring_quality_of_a_classifier.ipynb
+++ b/04_measuring_quality_of_a_classifier.ipynb
@@ -192,7 +192,7 @@
     "\n",
     "### Optional exercise\n",
     "\n",
-    "1.2 Assume the previously described test also produces wrong results on not-infected people, such that 5 out of 10000 will be diagnosed as infected. Compute the confusion matrix and the accuracy of this test."
+    "1.3 Assume the previously described test also produces wrong results on not-infected people, such that 5 out of 10000 will be diagnosed as infected. Compute the confusion matrix and the accuracy of this test."
    ]
   },
   {