diff --git a/Autonomous driving application - Car detection - v1.ipynb b/Autonomous driving application - Car detection - v1.ipynb
index 413c973..62f128e 100644
--- a/Autonomous driving application - Car detection - v1.ipynb	
+++ b/Autonomous driving application - Car detection - v1.ipynb	
@@ -373,6 +373,7 @@
     "    - xi2 = minimum of the x2 coordinates of the two boxes\n",
     "    - yi2 = minimum of the y2 coordinates of the two boxes\n",
     "    \n",
+    "- In order to compute the intersection area, you need to make sure the height and width of the intersection are positive, otherwise the intersection area should be zero. Use max(height, 0) and max(width, 0).\n\n",
     "In this code, we use the convention that (0,0) is the top-left corner of an image, (1,0) is the upper-right corner, and (1,1) the lower-right corner. "
    ]
   },
@@ -396,11 +397,11 @@
     "\n",
     "    # Calculate the (y1, x1, y2, x2) coordinates of the intersection of box1 and box2. Calculate its Area.\n",
     "    ### START CODE HERE ### (≈ 5 lines)\n",
-    "    xi1 = np.max([box1[0], box2[0]])\n",
-    "    yi1 = np.max([box1[1], box2[1]])\n",
-    "    xi2 = np.min([box1[2], box2[2]])\n",
-    "    yi2 = np.min([box1[3], box2[3]])\n",
-    "    inter_area = (yi2 - yi1) * (xi2 - xi1)\n",
+    "    xi1 = max(box1[0], box2[0])\n",
+    "    yi1 = max(box1[1], box2[1])\n",
+    "    xi2 = min(box1[2], box2[2])\n",
+    "    yi2 = min(box1[3], box2[3])\n",
+    "    inter_area = max((yi2 - yi1), 0) * max((xi2 - xi1), 0)\n",
     "    ### END CODE HERE ###    \n",
     "\n",
     "    # Calculate the Union area by using Formula: Union(A,B) = A + B - Inter(A,B)\n",