OOOOOH! It sounds like the obvious answer is 3 -- after all, if you have 1 black and 1 white, the third would have to be either black or white... but who said they were all the same kind of sock?!?! What if you had 25 DIFFERENT pairs of white socks, and 25 DIFFERENT pairs of black socks? And you had to find two of a set? Or even 50 mismatched white socks, and 48 mismatched black socks with a single pair of matching black socks? You'd have to pull out all 100 socks to be guaranteed a matching pair.