Update Chapter_2.ipynb (#224)

2E3.  It should be Option # 4 (I believe #3 is a typo).

Author: vntkumar8

Rethinking_2/End_of_chapter_problems/Chapter_2.ipynb

@@ -94,7 +94,7 @@
     "#### Answer \n",
     "\n",
     "\n",
-    "   (1) $Pr(Monday|rain)$ & (3) $\\frac{Pr(rain|Monday)Pr(Monday)}{Pr(rain)}$\n",
+    "   (1) $Pr(Monday|rain)$ & (4) $\\frac{Pr(rain|Monday)Pr(Monday)}{Pr(rain)}$\n",
     "\n",
     "### 2E4.\n",
     "\n",