John has 5 more 20-cent coins than 10-cent coins. After he used 12 of his 20-cent coins, the total value of 20-cent coins is $4.80 more than the total value of 10-cent coins. How many coins did he have at first?
|
20¢ |
10¢ |
Before |
1 u + 5 |
1 u |
Change |
- 12 |
|
After |
1 u - 7 |
1 u |
|
20¢ |
10¢ |
Number |
1 u - 7 |
1 u |
Value |
20 |
10 |
Total value |
20 u - 140 |
10 u |
$1 = 100¢
$4.80 = 480¢
Number of 20¢ coins in the end
= 1 u + 5 - 12
= 1 u - 7
Total value of 20¢ coins in the end
= 20 x (1 u - 7)
= 20 u - 140
Total value of 10¢ coins in the end
= 10 x 1 u
= 10 u
After using 12 20-cent coins, the value of 20-cent coins is 480¢ more than the value of 10-cent coins. If another 480¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.
20 u - 140 = 10 u + 480
20 u - 10 u = 480 + 140
10 u = 620
1 u = 620 ÷ 10 = 62
Number of coins that John had at first
= 1 u + 1 u + 5
= 2 u + 5
= (2 x 62) + 5
= 124 + 5
= 129
Answer(s): 129