Someone asked this question:
Compute the number of subsets of a set $A := \{1,2,...,11\}$ that contain the same number of even and odd values, e.g. the subsets $\{\}$,$\{1,2,5,8\}$ and $\{3,5,8,10\}$ should be counted, but the subsets $\{1,2,3\}$, $\{1,2,3,5,6\}$ and $\{1,2,...,11\}$ shouldn't.
and a person replied with this answer:
$\{1,3,5,7,9,11\}$, $\{2,4,6,8,10\}$ $$ {6 \choose 0}{5 \choose 0}+{6 \choose 1}{5 \choose 1}+{6 \choose 2}{5 \choose 2}+{6 \choose 3}{5 \choose 3}+{6 \choose 4}{5 \choose 4}+{6 \choose 5}{5 \choose 5} = $$ $$=1 + 30 +150 + 200 + 75 + 6 = 462$$
could someone please explain how this was worked out, because i don't understand.