Lee has 5 more 20-cent coins than 10-cent coins. After he used 16 of his 20-cent coins, the total value of 20-cent coins is $2.80 more than the total value of 10-cent coins. How many coins did he have in the end?

	20¢	10¢
Before	1 u + 5	1 u
Change	- 16
After	1 u - 11	1 u

	20¢	10¢
Number	1 u - 11	1 u
Value	20	10
Total value	20 u - 220	10 u

$1 = 100¢
$2.80 = 280¢

Number of 20¢ coins in the end
= 1 u + 5 - 16
= 1 u - 11

Total value of 20¢ coins in the end
= 20 x (1 u - 11)
= 20 u - 220

Total value of 10¢ coins in the end
= 10 x 1 u
= 10 u

After using 16 20-cent coins, the value of 20-cent coins is 280¢ more than the value of 10-cent coins. If another 280¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.

20 u - 220 = 10 u + 280
20 u - 10 u = 280 + 220
10 u = 500

1 u = 500 ÷ 10 = 50

Number of coins that Lee had in the end
= 1 u + 1 u - 11
= 2 u - 11
= (2 x 50) - 11
= 100 - 11
= 89

Answer(s): 89