Harry has 3 more 10-cent coins than 5-cent coins. After he used 16 of his 10-cent coins, the total value of 10-cent coins is $4.20 more than the total value of 5-cent coins. How many coins did he have in the end?

	10¢	5¢
Before	1 u + 3	1 u
Change	- 16
After	1 u - 13	1 u

	10¢	5¢
Number	1 u - 13	1 u
Value	10	5
Total value	10 u - 130	5 u

$1 = 100¢
$4.20 = 420¢

Number of 10¢ coins in the end
= 1 u + 3 - 16
= 1 u - 13

Total value of 10¢ coins in the end
= 10 x (1 u - 13)
= 10 u - 130

Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u

After using 16 10-cent coins, the value of 10-cent coins is 420¢ more than the value of 5-cent coins. If another 420¢ is added to the 5-cent coins, the total value of 10-cent coins and 5-cent coins will be the same.

10 u - 130 = 5 u + 420
10 u - 5 u = 420 + 130
5 u = 550

1 u = 550 ÷ 5 = 110

Number of coins that Harry had in the end
= 1 u + 1 u - 13
= 2 u - 13
= (2 x 110) - 13
= 220 - 13
= 207

Answer(s): 207