I have 2 coins, how much money might I have?
How many different amounts might I have?
List the possible combinations of
1, 5, 10, 25, 50 and 100 cent coins, in pairs, with the order unimportant. (A penny and a nickel is the same as a nickel and a penny, for example).
I get the number of possibilities to be 6+5+4+3+2+1= 7*6/2 = 21