⁹₁₀ of David's savings comprised of 20-cent coins and 50-cent coins. David used some 20-cent coins to purchase a toy car. The number of 50-cent coins left was 40% more than the number of 20-cent coins left. Given that David had 30 more 50-cent coins than 20-cent coins left in the end, find the amount of money David spent on the toy car.

	20-cent coins	50-cent coins
Before	9x7 = 63 u	1x7 = 7 u
Change	- 58 u
After	5x1 = 5 u	7x1 = 7 u

Fraction of David's savings that comprised of 50-cent coins
= 1 - ⁹₁₀
= ¹₁₀

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 1 and 7 is 7.

Number of more 50-cent coins than 20-cent coins
= 7 u - 5 u
= 2 u

2 u = 30

1 u = 30 ÷ 2 = 15

Number of 20-cent coins spent on the toy car 
= 63 u - 5 u
= 58 u
= 58 x 15
= 870

Amount that David spent on the toy car 
= 870 x 0.2
= $174

Answer(s): $174