At first, Mark, Sean and David had the same amount of money. After David spent some of his money, Mark spent ²₅ of his money and Sean spent ²₃ of his money, Mark had $76 more than Sean. In the end, the total amount of money the three boys had left was $392. How much money did David spend?

	Mark	Sean	David	Total
Before	5x3 =  15 u	3x5 = 15 u	15 u
Change	- 2x3 = - 6 u	- 2x5 = - 10 u	- ?
After	3x3 = 9 u	1x5 = 5 u		$392

The amount that Mark and Sean 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 Mark had more than Sean in the end
= 9 u - 5 u
= 4 u

4 u = 76

1 u = 76 ÷ 4 = 19

Amount that Mark and Sean had in the end
= 9 u + 5 u
= 14 u
= 14 x 19
= $266

Amount that David had in the end
= 392 - 266
= $126

Amount that David had at first
= 15 u
= 15 x 19
= $285

Amount that David spent
= 285 - 126
= $159

Answer(s): $159