Oliver and Riordan had $145 and $89 respectively. Each of them bought a sweater and a shirt at the same price. The cost of the sweater was 4 times as much as the shirt. In the end, Oliver had 5 times as much money as Riordan. What was the difference between the cost of the shirt and the sweater?

	Oliver	Riordan	Difference
Before	$145	$89	$56
Change	- 5 p	- 5 p
After	5 u	1 u	4 u

Since Oliver and Riordan bought the same items at the same price, the difference in the amounts they had remains unchanged at first and in the end.

5 u - 1 u = 145 - 89
4 u = 56

1 u = 56 ÷ 4 = 14

Cost of 1 sweater = 4 p
Cost of 1 shirt = 1 p

Total cost of 1 sweater and 1 shirt
= 4 p + 1 p
= 5 p

5 p = 89 - 14
5 p = 75

1 p = 75 ÷ 5 = 15

Difference in the cost between the sweater and the shirt
= 4 p - 1 p
= 3 p
= 3 x 15
= $45

Answer(s): $45