diff --git a/class_materials/exercises/particle_update_position.ipynb b/class_materials/exercises/particle_update_position.ipynb
index 8131b23..0a2772c 100644
--- a/class_materials/exercises/particle_update_position.ipynb
+++ b/class_materials/exercises/particle_update_position.ipynb
@@ -17,7 +17,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 10,
    "metadata": {
     "ExecuteTime": {
      "end_time": "2018-07-27T15:05:51.531289Z",
@@ -35,7 +35,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 11,
    "metadata": {
     "pycharm": {
      "name": "#%%\n"
@@ -70,7 +70,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [
     {
@@ -89,7 +89,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [
     {
@@ -98,13 +98,14 @@
        "8.28"
       ]
      },
-     "execution_count": 8,
+     "execution_count": 13,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "particle.position"
+    "dt=0.1\n",
+    "particle.update_position(dt)"
    ]
   },
   {