Simon has 10 more 20-cent coins than 10-cent coins. After he used 17 of his 20-cent coins, the total value of 20-cent coins is $2.70 more than the total value of 10-cent coins. How many coins did he have in the end?

	20¢	10¢
Before	1 u + 10	1 u
Change	- 17
After	1 u - 7	1 u

	20¢	10¢
Number	1 u - 7	1 u
Value	20	10
Total value	20 u - 140	10 u

$1 = 100¢
$2.70 = 270¢

Number of 20¢ coins in the end
= 1 u + 10 - 17
= 1 u - 7

Total value of 20¢ coins in the end
= 20 x (1 u - 7)
= 20 u - 140

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

After using 17 20-cent coins, the value of 20-cent coins is 270¢ more than the value of 10-cent coins. If another 270¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.

20 u - 140 = 10 u + 270
20 u - 10 u = 270 + 140
10 u = 410

1 u = 410 ÷ 10 = 41

Number of coins that Simon had in the end
= 1 u + 1 u - 7
= 2 u - 7
= (2 x 41) - 7
= 82 - 7
= 75

Answer(s): 75