17 coins is a lot for so little money. What if they all were pennies? Then we would have 17¢, 4¢ away from what we need. Changing one penny to a nickel adds four cents to our total (minus one cent from the penny, plus five from the nickel equals 4) So he found 16 pennies and one nickel.
penny = 1¢
nickel= 5¢
