⁵₈ of Luis's savings comprised of 10-cent coins and 20-cent coins. Luis used some 10-cent coins to purchase a mini plane. The number of 20-cent coins left was 40% more than the number of 10-cent coins left. Given that Luis had 108 more 20-cent coins than 10-cent coins left in the end, find the amount of money Luis spent on the mini plane.

	10-cent coins	20-cent coins
Before	5x7 = 35 u	3x7 = 21 u
Change	- 20 u
After	5x3 = 15 u	7x3 = 21 u

Fraction of Luis's savings that comprised of 20-cent coins
= 1 - ⁵₈
= ³₈

Number of 20-cents coins in the end in percentage
= 100% + 40%
= 140%

140% = ¹⁴⁰₁₀₀ = ⁷₅

Number of 20-cent coins remains unchanged. Make the number of 20-cent coins the same.  LCM of 3 and 7 is 21.

Number of more 20-cent coins than 10-cent coins
= 21 u - 15 u
= 6 u

6 u = 108

1 u = 108 ÷ 6 = 18

Number of 10-cent coins spent on the mini plane 
= 35 u - 15 u
= 20 u
= 20 x 18
= 360

Amount that Luis spent on the mini plane 
= 360 x 0.1
= $36

Answer(s): $36