At first, David, Charlie and Riordan had the same amount of money. After Riordan spent some of his money, David spent ²₅ of his money and Charlie spent ²₃ of his money, David had $108 more than Charlie. In the end, the total amount of money the three boys had left was $452. How much money did Riordan spend?

	David	Charlie	Riordan	Total
Before	5x3 =  15 u	3x5 = 15 u	15 u
Change	- 2x3 = - 6 u	- 2x5 = - 10 u	- ?
After	3x3 = 9 u	1x5 = 5 u		$452

The amount that David and Charlie each had at first is the same.  Make the amount that they each had the same.  LCM of 5 and 3 is 15.

Amount that David had more than Charlie in the end
= 9 u - 5 u
= 4 u

4 u = 108

1 u = 108 ÷ 4 = 27

Amount that David and Charlie had in the end
= 9 u + 5 u
= 14 u
= 14 x 27
= $378

Amount that Riordan had in the end
= 452 - 378
= $74

Amount that Riordan had at first
= 15 u
= 15 x 27
= $405

Amount that Riordan spent
= 405 - 74
= $331

Answer(s): $331