Question

Charles owed $390 to his friend. On the first day Charles paid his friend $12. Each following week the amount Charles paid his friend increased by the same amount. After 10 payments, Charles had paid back the full amount. By how much did each payment increase?

Answer 1

Hello! Ok, so this is the formula x10 + 12 = 390 =
x10 + 12 - 12 = 390 - 12 = 378 =
x10 = 378 =
x10 / 10 = 378 / 10 =
x = 37.80$
He paid 37.80$ per payment