Archie and Billy had $128 and $113 respectively. Each of them bought a cardigan and a blouse at the same price. The cost of the cardigan was 3 times as much as the blouse. In the end, Archie had 4 times as much money as Billy. What was the difference between the cost of the blouse and the cardigan?

	Archie	Billy	Difference
Before	$128	$113	$15
Change	- 4 p	- 4 p
After	4 u	1 u	3 u

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

4 u - 1 u = 128 - 113
3 u = 15

1 u = 15 ÷ 3 = 5

Cost of 1 cardigan = 3 p
Cost of 1 blouse = 1 p

Total cost of 1 cardigan and 1 blouse
= 3 p + 1 p
= 4 p

4 p = 113 - 5
4 p = 108

1 p = 108 ÷ 4 = 27

Difference in the cost between the cardigan and the blouse
= 3 p - 1 p
= 2 p
= 2 x 27
= $54

Answer(s): $54