Ken has 6 more 20-cent coins than 5-cent coins. After he used 9 of his 20-cent coins, the total value of 20-cent coins is $4.20 more than the total value of 5-cent coins. How many coins did he have in the end?
| |
20¢ |
5¢ |
| Before |
1 u + 6 |
1 u |
| Change |
- 9 |
|
| After |
1 u - 3 |
1 u |
| |
20¢ |
5¢ |
| Number |
1 u - 3 |
1 u |
| Value |
20 |
5 |
| Total value |
20 u - 60 |
5 u |
$1 = 100¢
$4.20 = 420¢
Number of 20¢ coins in the end
= 1 u + 6 - 9
= 1 u - 3
Total value of 20¢ coins in the end
= 20 x (1 u - 3)
= 20 u - 60
Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u
After using 9 20-cent coins, the value of 20-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 20-cent coins and 5-cent coins will be the same.
20 u - 60 = 5 u + 420
20 u - 5 u = 420 + 60
15 u = 480
1 u = 480 ÷ 15 = 32
Number of coins that Ken had in the end
= 1 u + 1 u - 3
= 2 u - 3
= (2 x 32) - 3
= 64 - 3
= 61
Answer(s): 61
