Ten Red socks and ten blue socks are all mixed up in a dresser drawer. The twenty socks are exactly alike except for their color. The room in in pitch darkness and you want two matching socks. What is the smallest number of socks you must take out of the drawer in order to be certain that you have a pair that match? (source: Entertaining Mathematical Puzzles By Martin Gardner, Anthony Ravielli)
Answer:
Many people (including me) initially (and incorrectly )solved this puzzle as follows:
* Initially I pull out a sock, and this could be Red / Blue.
* Then to match the color of the first sock, we pull out (10 + 1) socks.
But if we read the question carefully, it simply says, "pair that match" and nothing about the
color, so all we need is to pull out just three socks.
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