At first, Liam, Seth and Oliver had the same amount of money. After Oliver spent some of his money, Liam spent ³₇ of his money and Seth spent ³₅ of his money, Liam had $84 more than Seth. In the end, the total amount of money the three boys had left was $561. How much money did Oliver spend?

	Liam	Seth	Oliver	Total
Before	7x5 =  35 u	5x7 = 35 u	35 u
Change	- 3x5 = - 15 u	- 3x7 = - 21 u	- ?
After	4x5 = 20 u	2x7 = 14 u		$561

The amount that Liam and Seth each had at first is the same.  Make the amount that they each had the same.  LCM of 7 and 5 is 35.

Amount that Liam had more than Seth in the end
= 20 u - 14 u
= 6 u

6 u = 84

1 u = 84 ÷ 6 = 14

Amount that Liam and Seth had in the end
= 20 u + 14 u
= 34 u
= 34 x 14
= $476

Amount that Oliver had in the end
= 561 - 476
= $85

Amount that Oliver had at first
= 35 u
= 35 x 14
= $490

Amount that Oliver spent
= 490 - 85
= $405

Answer(s): $405