You are in a pitch black room and need to get a pair of socks out of your drawer which can contain up to 100 socks. In the drawer is a mixture of black and white socks, and there's at least one pair of either color. If you choose two socks, the chance that you draw out a black pair is 2/3.
What is the chance that you draw out a white pair?
Bonus: what would the answer be if the drawer contained between 100 and 1000 socks?
The required chance of getting a white pair is 9/297.