Question

Johann borrows money from his parents to purchase a bike. He makes weekly payments to his parents to repay the money borrowed. The total amount of money repaid at the end of week n can be represented using the recursive formula an=10+an-1. At the end of the fourth week, Johann had repaid his parents a total of $55. What is the total amount Johann had repaid his parents at the end of the first week?
$10
$20
$25
$35

Answer 1

Each week he adds $10, so a_n = a_1 + (n-1)·10. With a_4 = 55:

a_1 = 55 − 3·10 = 55 − 30 = $25.

Answer: $25.