There are 53 dimes in Jonahs piggy bank. You must use algebra to solve for a variable X as follows:
x.10+(91-X).05=7.2
Solving through will yield X =53 which means 91 - 53 = 38.
53*.10 + 38*.05 = $7.20.
Other methods will also work, but this is the most straight forward.
