Update Exercises-4.ipynb (brandon-rhodes#31)

Fix several more typos

Author: Bonifacio2

Exercises-4.ipynb

@@ -378,7 +378,7 @@
       }
     }, 
     {
-      "source": "### Plot the fraction of roles that have been 'actor' roles each year in the hitsory of film.", 
+      "source": "### Plot the fraction of roles that have been 'actor' roles each year in the history of film.", 
       "cell_type": "markdown", 
       "metadata": {
         "collapsed": true
@@ -472,4 +472,4 @@
       }
     }
   }
-}
+}

Solutions-1.ipynb

@@ -1762,7 +1762,7 @@
     }
    ],
    "source": [
-    "# How many roles were avilable for actresses in the 1950s?\n",
+    "# How many roles were available for actresses in the 1950s?\n",
     "\n",
     "c = cast\n",
     "c = c[c.year // 10 == 195]\n",

Solutions-4.ipynb

@@ -517,7 +517,7 @@
    ],
    "source": [
     "# Plot the fraction of roles that have been 'actor' roles\n",
-    "# each year in the hitsory of film.\n",
+    "# each year in the history of film.\n",
     "\n",
     "c = cast\n",
     "c = c.groupby(['year', 'type']).size()\n",