Fred has 7 more 10-cent coins than 5-cent coins. After he used 18 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 at first?
|
10¢ |
5¢ |
Before |
1 u + 7 |
1 u |
Change |
- 18 |
|
After |
1 u - 11 |
1 u |
|
10¢ |
5¢ |
Number |
1 u - 11 |
1 u |
Value |
10 |
5 |
Total value |
10 u - 110 |
5 u |
$1 = 100¢
$3.20 = 320¢
Number of 10¢ coins in the end
= 1 u + 7 - 18
= 1 u - 11
Total value of 10¢ coins in the end
= 10 x (1 u - 11)
= 10 u - 110
Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u
After using 18 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 - 110 = 5 u + 320
10 u - 5 u = 320 + 110
5 u = 430
1 u = 430 ÷ 5 = 86
Number of coins that Fred had at first
= 1 u + 1 u + 7
= 2 u + 7
= (2 x 86) + 7
= 172 + 7
= 179
Answer(s): 179