Question

Chelsea has four loose socks in her sock drawer - 2 black socks and 2 white socks. If Chelsea is getting out socks in a dark room and she does not care whether she has a black pair or a white pair, how many socks must she get from the drawer to be sure that she has two that match?

Answer 1

after she retrieves either a black or a white sock   she has a  one in 3 chance of retrieving the same coloured sock.
So with 2 socks retrieved  we cant be sure she has 2 that match.

Picking a third sock:-

If the first 2 match  then  she will have a pair.

If the first 2 were different  then whatever one she picks there must be a match

So the answer is 3 socks from the drawer.

Answer 2

Chelsea must get three socks in order to have a pair.