At first, Pierre, Sam and Oliver had the same amount of money. After Oliver spent some of his money, Pierre spent ²₇ of his money and Sam spent ¹₂ of his money, Pierre had $39 more than Sam. In the end, the total amount of money the three boys had left was $418. How much money did Oliver spend?

	Pierre	Sam	Oliver	Total
Before	7x2 =  14 u	2x7 = 14 u	14 u
Change	- 2x2 = - 4 u	- 1x7 = - 7 u	- ?
After	5x2 = 10 u	1x7 = 7 u		$418

The amount that Pierre and Sam 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 Pierre had more than Sam in the end
= 10 u - 7 u
= 3 u

3 u = 39

1 u = 39 ÷ 3 = 13

Amount that Pierre and Sam had in the end
= 10 u + 7 u
= 17 u
= 17 x 13
= $221

Amount that Oliver had in the end
= 418 - 221
= $197

Amount that Oliver had at first
= 14 u
= 14 x 13
= $182

Amount that Oliver spent
= 182 - 197
= $-15

Answer(s): $-15