⁵₇ of Wesley's savings comprised of 20-cent coins and 50-cent coins. Wesley used some 20-cent coins to purchase a mini-helicopter. The number of 50-cent coins left was 40% more than the number of 20-cent coins left. Given that Wesley had 12 more 50-cent coins than 20-cent coins left in the end, find the amount of money Wesley spent on the mini-helicopter.

	20-cent coins	50-cent coins
Before	5x7 = 35 u	2x7 = 14 u
Change	- 25 u
After	5x2 = 10 u	7x2 = 14 u

Fraction of Wesley's savings that comprised of 50-cent coins
= 1 - ⁵₇
= ²₇

Number of 50-cents coins in the end in percentage
= 100% + 40%
= 140%

140% = ¹⁴⁰₁₀₀ = ⁷₅

Number of 50-cent coins remains unchanged. Make the number of 50-cent coins the same.  LCM of 2 and 7 is 14.

Number of more 50-cent coins than 20-cent coins
= 14 u - 10 u
= 4 u

4 u = 12

1 u = 12 ÷ 4 = 3

Number of 20-cent coins spent on the mini-helicopter 
= 35 u - 10 u
= 25 u
= 25 x 3
= 75

Amount that Wesley spent on the mini-helicopter 
= 75 x 0.2
= $15

Answer(s): $15