Rupert has a pair of red socks, a pair of green socks and a pair of blue socks in his drawer. If he takes two socks out at random, what is the chance that they are a pair? How many socks would he need to take out to be sure of getting a pair?
Solution:
After selecting the first sock, there are five remaining socks in the drawer and only one of these completes the pair. Therefore the chance of taking out a second sock at random and making a pair is 1/5.
Manu’s first three selections could be one of each colour (no pair) but his next pick must be the pair of one of the first three, so taking 4 socks would guarantee a pair.