Simon had $297 and Ryan had $139 at first. Each of them bought an identical sweater and an identical skirt from the same shop. The skirt cost 5 times as much as the sweater. In the end, Simon had 3 times as much money as Ryan. What was the cost of the sweater?

	Simon	Ryan	Difference
Before	$297	$139	$158
Change	- 1 sweater - 1 skirt	- 1 sweater - 1 skirt
After	3 u	1 u	2 u

Since Simon and Ryan bought the same items, the difference  in their amounts remains the same.

Difference in the amounts that they had
= 3 u - 1 u
= 2 u

2 u = 297 - 139
2 u = 158

1 u = 158 ÷ 2 = 79

Amount that Ryan had in the end
= 1 u
= $79

Cost of 1 sweater and 1 skirt
= 139 - 1 u
= 139 - 79
= $60

The skirt cost 5 times as much as the sweater.

Cost of 1 sweater = 1 p
Cost of 1 skirt = 5 p

Total cost of 1 sweater and 1 skirt
= 1 p + 5 p
= 6 p

6 p = 60

1 p = 60 ÷ 6 = 10

Cost of the sweater
= 1 p
= $10

Answer(s): $10