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?

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.

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