Andy and Diana both got some pocket money from their aunt.
Andy spent all his money on collector's coins, he bought 5 of them.
Diana bought 3 of such coins, and she brought home 20 dollars of change.
after they came home their sister said "hah! I bet you I can find out how much each coin costs even if you don't tell me how much money your aunt gave you, if she gave you both the same amount!"
