Update pandas intro notebook (#40)

Author: jorisvandenbossche

_solved/01-introduction-tabular-data.ipynb

@@ -1052,7 +1052,7 @@
     "editable": true
    },
    "source": [
-    "Pandas provides a large set of **summary** functions that operate on different kinds of pandas objects (DataFrames, Series, Index) and produce single value. When applied to a DataFrame, the result is returned as a pandas Series (one value for each column). "
+    "Pandas provides a large set of **summary** functions that operate on different kinds of pandas objects (DataFrames, Series, Index) and produce a single value. When applied to a DataFrame, the result is returned as a pandas Series (one value for each column). "
    ]
   },
   {
@@ -2280,7 +2280,7 @@
     "\\>       | Greater than\n",
     "\\>=       | Greater than or equal\n",
     "<       | Lesser than\n",
-    "!=       | Lesser than or equal\n",
+    "<=       | Lesser than or equal\n",
     "\n",
     "and to combine multiple conditions:\n",
     "\n",
@@ -2639,7 +2639,7 @@
     "\n",
     "**EXERCISE**:\n",
     "\n",
-    "* What is the average popolation number of the districts?\n",
+    "* What is the average population number of the districts?\n",
     "* And what is the median?\n",
     "\n",
     "<details>\n",
@@ -3324,7 +3324,7 @@
     "\n",
     "**EXERCISE**:\n",
     "\n",
-    "* Select all rows for the districts of the 1st arrondissement.\n",
+    "* Select all rows for the districts of the 3rd arrondissement.\n",
     "* For this subset, what is the total population of the arrondissement?\n",
     "    \n",
     "</div>"
@@ -4209,7 +4209,7 @@
     "editable": true
    },
    "source": [
-    "This is only an ultra short intro to matplotlib. In the course materials, you can find another notebook with some more details ([visualization_01_matplotlib.ipynb](visualization_01_matplotlib.ipynb#An-small-cheat-sheet-reference-for-some-common-elements))."
+    "This is only an ultra short intro to matplotlib. In the course materials, you can find another notebook with some more details ([visualization-01-matplotlib.ipynb](visualization_01_matplotlib.ipynb#An-small-cheat-sheet-reference-for-some-common-elements))."
    ]
   },
   {
@@ -4225,7 +4225,7 @@
     "\n",
     "Galleries are great to get inspiration, see the plot you want, and check the code how it is created:\n",
     "    \n",
-    "* [matplotlib gallery](http://matplotlib.org/gallery.html\") is an important resource to start from\n",
+    "* [matplotlib gallery](http://matplotlib.org/gallery.html) is an important resource to start from\n",
     "* [seaborn gallery](https://seaborn.pydata.org/examples/index.html)\n",
     "* The Python Graph Gallery (https://python-graph-gallery.com/)\n",
     "\n",