Riordan had $312 and Nick had $120 at first. Each of them bought an identical shirt and an identical coat from the same shop. The coat cost 5 times as much as the shirt. In the end, Riordan had 3 times as much money as Nick. What was the cost of the shirt?

	Riordan	Nick	Difference
Before	$312	$120	$192
Change	- 1 shirt - 1 coat	- 1 shirt - 1 coat
After	3 u	1 u	2 u

Since Riordan and Nick 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 = 312 - 120
2 u = 192

1 u = 192 ÷ 2 = 96

Amount that Nick had in the end
= 1 u
= $96

Cost of 1 shirt and 1 coat
= 120 - 1 u
= 120 - 96
= $24

The coat cost 5 times as much as the shirt.

Cost of 1 shirt = 1 p
Cost of 1 coat = 5 p

Total cost of 1 shirt and 1 coat
= 1 p + 5 p
= 6 p

6 p = 24

1 p = 24 ÷ 6 = 4

Cost of the shirt
= 1 p
= $4

Answer(s): $4