100 pennies are on a table. 10 are tails. With your eyes closed, how can you separate the pennies into 2 groups such that each group has the same number of tails?
If you have not tried to solve it, have a go now. For everyone else the answer is after the break.
Turn over any 10 pennies. These pennies form group 1. The rest of the pennies form group 2. Did you solve it?