A man wears socks of two colours - Black and brown. He has altogether 20 black socks and 20 brown socks in a drawer. Supposing he has to take out the socks in the dark, how many must he take out to be sure that he has a matching pair ?

Correct Answer: 3
Since there are socks of only two colours, so two out of any three socks must always be of the same colour.