²₃ of David's savings comprised of 5-cent coins and 50-cent coins. David used some 5-cent coins to purchase a doll set. The number of 50-cent coins left was 40% more than the number of 5-cent coins left. Given that David had 40 more 50-cent coins than 5-cent coins left in the end, find the amount of money David spent on the doll set.

	5-cent coins	50-cent coins
Before	2x7 = 14 u	1x7 = 7 u
Change	- 9 u
After	5x1 = 5 u	7x1 = 7 u

Fraction of David's savings that comprised of 50-cent coins
= 1 - ²₃
= ¹₃

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 5-cent coins
= 7 u - 5 u
= 2 u

2 u = 40

1 u = 40 ÷ 2 = 20

Number of 5-cent coins spent on the doll set 
= 14 u - 5 u
= 9 u
= 9 x 20
= 180

Amount that David spent on the doll set 
= 180 x 0.05
= $9

Answer(s): $9