diff --git a/pandas/pandas.ipynb b/pandas/pandas.ipynb
index f8ec177..5c66bf4 100644
--- a/pandas/pandas.ipynb
+++ b/pandas/pandas.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:207ce6e6163805a40ff6b55987e709194f2be605d9cc8f7276e2b6d50b096e89"
+  "signature": "sha256:f58e882e3019ecb243505ef140cb0aedee21ecd47d1210ca8e6b4e2281c1316e"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -18,7 +18,8 @@
       "* DataFrame\n",
       "* Reindexing\n",
       "* Dropping Entries\n",
-      "* Indexing, Selecting, Filtering"
+      "* Indexing, Selecting, Filtering\n",
+      "* Arithmetic and Data Alignment"
      ]
     },
     {
@@ -26,7 +27,8 @@
      "collapsed": false,
      "input": [
       "from pandas import Series, DataFrame\n",
-      "import pandas as pd"
+      "import pandas as pd\n",
+      "import numpy as np"
      ],
      "language": "python",
      "metadata": {},
@@ -3319,14 +3321,100 @@
      ],
      "prompt_number": 63
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "## Arithmetic and Data Alignment"
+     ]
+    },
     {
      "cell_type": "code",
      "collapsed": false,
-     "input": [],
+     "input": [
+      "ser_6 = Series(np.random.randn(5),\n",
+      "               index=['a', 'b', 'c', 'd', 'e'])\n",
+      "ser_6\n"
+     ],
      "language": "python",
      "metadata": {},
-     "outputs": [],
-     "prompt_number": 63
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 64,
+       "text": [
+        "a   -0.224292\n",
+        "b   -1.166149\n",
+        "c   -2.078194\n",
+        "d    2.060130\n",
+        "e    0.292102\n",
+        "dtype: float64"
+       ]
+      }
+     ],
+     "prompt_number": 64
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "ser_7 = Series(np.random.randn(5),\n",
+      "               index=['a', 'c', 'e', 'f', 'g'])\n",
+      "ser_7"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 65,
+       "text": [
+        "a   -0.329560\n",
+        "c    1.009019\n",
+        "e   -2.489898\n",
+        "f   -0.731142\n",
+        "g   -0.025979\n",
+        "dtype: float64"
+       ]
+      }
+     ],
+     "prompt_number": 65
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Adding objects results in the union of index pairs if the pairs are not the same, resulting in NAs for indices that do not overlap:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "ser_6 + ser_7"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 66,
+       "text": [
+        "a   -0.553851\n",
+        "b         NaN\n",
+        "c   -1.069176\n",
+        "d         NaN\n",
+        "e   -2.197796\n",
+        "f         NaN\n",
+        "g         NaN\n",
+        "dtype: float64"
+       ]
+      }
+     ],
+     "prompt_number": 66
     }
    ],
    "metadata": {}