Tim has 2 more 20-cent coins than 5-cent coins. After he used 7 of his 20-cent coins, the total value of 20-cent coins is $4.70 more than the total value of 5-cent coins. How many coins did he have in the end?
| |
20¢ |
5¢ |
| Before |
1 u + 2 |
1 u |
| Change |
- 7 |
|
| After |
1 u - 5 |
1 u |
| |
20¢ |
5¢ |
| Number |
1 u - 5 |
1 u |
| Value |
20 |
5 |
| Total value |
20 u - 100 |
5 u |
$1 = 100¢
$4.70 = 470¢
Number of 20¢ coins in the end
= 1 u + 2 - 7
= 1 u - 5
Total value of 20¢ coins in the end
= 20 x (1 u - 5)
= 20 u - 100
Total value of 5¢ coins in the end
= 5 x 1 u
= 5 u
After using 7 20-cent coins, the value of 20-cent coins is 470¢ more than the value of 5-cent coins. If another 470¢ is added to the 5-cent coins, the total value of 20-cent coins and 5-cent coins will be the same.
20 u - 100 = 5 u + 470
20 u - 5 u = 470 + 100
15 u = 570
1 u = 570 ÷ 15 = 38
Number of coins that Tim had in the end
= 1 u + 1 u - 5
= 2 u - 5
= (2 x 38) - 5
= 76 - 5
= 71
Answer(s): 71
