At first, Justin, Tom and Gabriel had the same amount of money. After Gabriel spent some of his money, Justin spent ²₇ of his money and Tom spent ¹₂ of his money, Justin had $78 more than Tom. In the end, the total amount of money the three boys had left was $489. How much money did Gabriel spend?

	Justin	Tom	Gabriel	Total
Before	7x2 =  14 u	2x7 = 14 u	14 u
Change	- 2x2 = - 4 u	- 1x7 = - 7 u	- ?
After	5x2 = 10 u	1x7 = 7 u		$489

The amount that Justin and Tom each had at first is the same.  Make the amount that they each had the same.  LCM of 7 and 2 is 14.

Amount that Justin had more than Tom in the end
= 10 u - 7 u
= 3 u

3 u = 78

1 u = 78 ÷ 3 = 26

Amount that Justin and Tom had in the end
= 10 u + 7 u
= 17 u
= 17 x 26
= $442

Amount that Gabriel had in the end
= 489 - 442
= $47

Amount that Gabriel had at first
= 14 u
= 14 x 26
= $364

Amount that Gabriel spent
= 364 - 47
= $317

Answer(s): $317