⁹₁₀ of Oscar's savings comprised of 10-cent coins and 20-cent coins. Oscar used some 10-cent coins to purchase a kitchen set. The number of 20-cent coins left was 40% more than the number of 10-cent coins left. Given that Oscar had 10 more 20-cent coins than 10-cent coins left in the end, find the amount of money Oscar spent on the kitchen set.

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

Fraction of Oscar's savings that comprised of 20-cent coins
= 1 - ⁹₁₀
= ¹₁₀

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 1 and 7 is 7.

Number of more 20-cent coins than 10-cent coins
= 7 u - 5 u
= 2 u

2 u = 10

1 u = 10 ÷ 2 = 5

Number of 10-cent coins spent on the kitchen set 
= 63 u - 5 u
= 58 u
= 58 x 5
= 290

Amount that Oscar spent on the kitchen set 
= 290 x 0.1
= $29

Answer(s): $29