Can you find a set of cards among these six, such that the socks on the chosen cards can be grouped into matching pairs? (Duplicate pairs of the same sock are OK) Spoilers: If the cards are indexed as 1 2 3 4 5 6 Then the following three subsets work: $\ 1, 2, 4, 5, 6 \$, $\ 2, 3, 6 \$, and $\ 1, 3, 4, 5 \$.