⁴₇ of Mark's savings comprised of 5-cent coins and 20-cent coins. Mark used some 5-cent coins to purchase a doll set. The number of 20-cent coins left was 40% more than the number of 5-cent coins left. Given that Mark had 120 more 20-cent coins than 5-cent coins left in the end, find the amount of money Mark spent on the doll set.

	5-cent coins	20-cent coins
Before	4x7 = 28 u	3x7 = 21 u
Change	- 13 u
After	5x3 = 15 u	7x3 = 21 u

Fraction of Mark's savings that comprised of 20-cent coins
= 1 - ⁴₇
= ³₇

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 5-cent coins
= 21 u - 15 u
= 6 u

6 u = 120

1 u = 120 ÷ 6 = 20

Number of 5-cent coins spent on the doll set 
= 28 u - 15 u
= 13 u
= 13 x 20
= 260

Amount that Mark spent on the doll set 
= 260 x 0.05
= $13

Answer(s): $13