Question 23
Noppon chooses two different numbers from $\{11,12,13,\ldots,20,21\}$. The probability that their sum is even is $\frac{m}{n}$. Find $m+n$.
Assume all pairs of distinct numbers are equally likely, and write m/n in lowest terms with positive integers m and n. The source omits the lowest-terms condition.
Assume all pairs of distinct numbers are equally likely, and write m/n in lowest terms with positive integers m and n. The source omits the lowest-terms condition.