Pierre has 9 more 50-cent coins than 5-cent coins. After he used 13 of his 50-cent coins, the total value of 50-cent coins is $3.40 more than the total value of 5-cent coins. How many coins did he have in the end?

	50¢	5¢
Before	1 u + 9	1 u
Change	- 13
After	1 u - 4	1 u

	50¢	5¢
Number	1 u - 4	1 u
Value	50	5
Total value	50 u - 200	5 u

$1 = 100¢
$3.40 = 340¢

Number of 50¢ coins in the end
= 1 u + 9 - 13
= 1 u - 4

Total value of 50¢ coins in the end
= 50 x (1 u - 4)
= 50 u - 200

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

After using 13 50-cent coins, the value of 50-cent coins is 340¢ more than the value of 5-cent coins. If another 340¢ is added to the 5-cent coins, the total value of 50-cent coins and 5-cent coins will be the same.

50 u - 200 = 5 u + 340
50 u - 5 u = 340 + 200
45 u = 540

1 u = 540 ÷ 45 = 12

Number of coins that Pierre had in the end
= 1 u + 1 u - 4
= 2 u - 4
= (2 x 12) - 4
= 24 - 4
= 20

Answer(s): 20