You have 10 pairs of socks, five black and five blue, but they are not paired up. Instead, they are all mixed up in a drawer. It’s early in the morning, and you don’t want to turn on the lights in your darkroom. How many socks must you pull out to guarantee that you have a pair of one colour? How many must you pull out to have two good pairs (each pair is the same colour)? How many must you pull out to be certain that you have a pair of black socks?