Fabian has 7 more 50-cent coins than 10-cent coins. After he used 18 of his 50-cent coins, the total value of 50-cent coins is $2.90 more than the total value of 10-cent coins. How many coins did he have in the end?

	50¢	10¢
Before	1 u + 7	1 u
Change	- 18
After	1 u - 11	1 u

	50¢	10¢
Number	1 u - 11	1 u
Value	50	10
Total value	50 u - 550	10 u

$1 = 100¢
$2.90 = 290¢

Number of 50¢ coins in the end
= 1 u + 7 - 18
= 1 u - 11

Total value of 50¢ coins in the end
= 50 x (1 u - 11)
= 50 u - 550

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

After using 18 50-cent coins, the value of 50-cent coins is 290¢ more than the value of 10-cent coins. If another 290¢ is added to the 10-cent coins, the total value of 50-cent coins and 10-cent coins will be the same.

50 u - 550 = 10 u + 290
50 u - 10 u = 290 + 550
40 u = 840

1 u = 840 ÷ 40 = 21

Number of coins that Fabian had in the end
= 1 u + 1 u - 11
= 2 u - 11
= (2 x 21) - 11
= 42 - 11
= 31

Answer(s): 31