Question

Your aunt bought a new car. After three months of car payments she owed a total of $22,275 to the bank for the car loan. After 12 months, she owed $18,900 to the bank for the car loan. What was her average payment rate on the principal of the car loan during this time?

Answer 1

The principal decreases by
  22275 -18900 = 3375
in those 9 months, so the average monthly principal payment is
  3375/9 = 375

Her average payment rate on the principal during this time is $375 per month.