⁷₉ of Japheth's savings comprised of 20-cent coins and 10-cent coins. Japheth used some 20-cent coins to purchase a doll set. The number of 10-cent coins left was 25% more than the number of 20-cent coins left. Given that Japheth had 10 more 10-cent coins than 20-cent coins left in the end, find the amount of money Japheth spent on the doll set.

	20-cent coins	10-cent coins
Before	7x5 = 35 u	2x5 = 10 u
Change	- 27 u
After	4x2 = 8 u	5x2 = 10 u

Fraction of Japheth's savings that comprised of 10-cent coins
= 1 - ⁷₉
= ²₉

Number of 10-cents coins in the end in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of 10-cent coins remains unchanged. Make the number of 10-cent coins the same.  LCM of 2 and 5 is 10.

Number of more 10-cent coins than 20-cent coins
= 10 u - 8 u
= 2 u

2 u = 10

1 u = 10 ÷ 2 = 5

Number of 20-cent coins spent on the doll set 
= 35 u - 8 u
= 27 u
= 27 x 5
= 135

Amount that Japheth spent on the doll set 
= 135 x 0.2
= $27

Answer(s): $27