Harry has 7 more 20-cent coins than 5-cent coins. After he used 13 of his 20-cent coins, the total value of 20-cent coins is $2.10 more than the total value of 5-cent coins. How many coins did he have at first?
| |
20¢ |
5¢ |
| Before |
1 u + 7 |
1 u |
| Change |
- 13 |
|
| After |
1 u - 6 |
1 u |
| |
20¢ |
5¢ |
| Number |
1 u - 6 |
1 u |
| Value |
20 |
5 |
| Total value |
20 u - 120 |
5 u |
$1 = 100¢
$2.10 = 210¢
Number of 20¢ coins in the end
= 1 u + 7 - 13
= 1 u - 6
Total value of 20¢ coins in the end
= 20 x (1 u - 6)
= 20 u - 120
Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u
After using 13 20-cent coins, the value of 20-cent coins is 210¢ more than the value of 5-cent coins. If another 210¢ is added to the 5-cent coins, the total value of 20-cent coins and 5-cent coins will be the same.
20 u - 120 = 5 u + 210
20 u - 5 u = 210 + 120
15 u = 330
1 u = 330 ÷ 15 = 22
Number of coins that Harry had at first
= 1 u + 1 u + 7
= 2 u + 7
= (2 x 22) + 7
= 44 + 7
= 51
Answer(s): 51
