Added clarification for a common mistake

src/chapters/1/sections/counting/problems/14.tex

@@ -6,4 +6,9 @@
 is $4 * 256 = 1024$.
 
 We wish to sample two pizzas, with replacement, out of the $1024$ possibilities.
-By Einstein-Bose, there are a total of $\binom{1025}{2}$ choices.
+By Einstein-Bose, there are a total of $\binom{1025}{2}$ choices.
+
+A common mistake is to use multiplication rule to get $(2^8)*(2^8)$ as 
+total possible combinations for two pizzas, and try to adjust for overcounting
+by dividing the result with 2 (as order between pizzas doesn't matter). This 
+fails because the possibilities with identical pizzas are counted only once.