Math & Logic · Ages 18+
Riddle #211
A drawer in a pitch-black room holds 10 black socks and 10 blue socks, identical except in colour. How many socks must you take out to be certain of a matching pair — and how many to be certain of a black pair?
You solved this one before
Open-ended riddle: think it through, then reveal the answer.
Answer: Three for a matching pair; twelve for a black pair.
Three socks can only be two colours, so two of them must match. But the worst case for black is drawing all 10 blue socks first, then 2 black ones — 12 in total.