Warren has 8 more 10-cent coins than 5-cent coins. After he used 15 of his 10-cent coins, the total value of 10-cent coins is $3.20 more than the total value of 5-cent coins. How many coins did he have in the end?
| |
10¢ |
5¢ |
| Before |
1 u + 8 |
1 u |
| Change |
- 15 |
|
| After |
1 u - 7 |
1 u |
| |
10¢ |
5¢ |
| Number |
1 u - 7 |
1 u |
| Value |
10 |
5 |
| Total value |
10 u - 70 |
5 u |
$1 = 100¢
$3.20 = 320¢
Number of 10¢ coins in the end
= 1 u + 8 - 15
= 1 u - 7
Total value of 10¢ coins in the end
= 10 x (1 u - 7)
= 10 u - 70
Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u
After using 15 10-cent coins, the value of 10-cent coins is 320¢ more than the value of 5-cent coins. If another 320¢ is added to the 5-cent coins, the total value of 10-cent coins and 5-cent coins will be the same.
10 u - 70 = 5 u + 320
10 u - 5 u = 320 + 70
5 u = 390
1 u = 390 ÷ 5 = 78
Number of coins that Warren had in the end
= 1 u + 1 u - 7
= 2 u - 7
= (2 x 78) - 7
= 156 - 7
= 149
Answer(s): 149
