Jonah has collected 91 coins worth $7.20 in his piggy bank. his collection includes only dimes and nickels. how many dimes are there in jonah's piggy bank?

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.