Luis has 3 more 50-cent coins than 20-cent coins. After he used 15 of his 50-cent coins, the total value of 50-cent coins is $3.60 more than the total value of 20-cent coins. How many coins did he have at first?

	50¢	20¢
Before	1 u + 3	1 u
Change	- 15
After	1 u - 12	1 u

	50¢	20¢
Number	1 u - 12	1 u
Value	50	20
Total value	50 u - 600	20 u

$1 = 100¢
$3.60 = 360¢

Number of 50¢ coins in the end
= 1 u + 3 - 15
= 1 u - 12

Total value of 50¢ coins in the end
= 50 x (1 u - 12)
= 50 u - 600

Total value of 20¢ coins in the end
= 20 x 1 u
= 20 u

After using 15 50-cent coins, the value of 50-cent coins is 360¢ more than the value of 20-cent coins. If another 360¢ is added to the 20-cent coins, the total value of 50-cent coins and 20-cent coins will be the same.

50 u - 600 = 20 u + 360
50 u - 20 u = 360 + 600
30 u = 960

1 u = 960 ÷ 30 = 32

Number of coins that Luis had at first
= 1 u + 1 u + 3
= 2 u + 3
= (2 x 32) + 3
= 64 + 3
= 67

Answer(s): 67