Oliver has 10 more 20-cent coins than 10-cent coins. After he used 15 of his 20-cent coins, the total value of 20-cent coins is $3.30 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 |
- 15 |
|
| After |
1 u - 5 |
1 u |
| |
20¢ |
10¢ |
| Number |
1 u - 5 |
1 u |
| Value |
20 |
10 |
| Total value |
20 u - 100 |
10 u |
$1 = 100¢
$3.30 = 330¢
Number of 20¢ coins in the end
= 1 u + 10 - 15
= 1 u - 5
Total value of 20¢ coins in the end
= 20 x (1 u - 5)
= 20 u - 100
Total value of 10¢ coins in the end
= 10 x 1 u
= 10 u
After using 15 20-cent coins, the value of 20-cent coins is 330¢ more than the value of 10-cent coins. If another 330¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.
20 u - 100 = 10 u + 330
20 u - 10 u = 330 + 100
10 u = 430
1 u = 430 ÷ 10 = 43
Number of coins that Oliver had in the end
= 1 u + 1 u - 5
= 2 u - 5
= (2 x 43) - 5
= 86 - 5
= 81
Answer(s): 81
