Michael has 6 more 20-cent coins than 10-cent coins. After he used 13 of his 20-cent coins, the total value of 20-cent coins is $2.90 more than the total value of 10-cent coins. How many coins did he have in the end?
| |
20¢ |
10¢ |
| Before |
1 u + 6 |
1 u |
| Change |
- 13 |
|
| 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¢
$2.90 = 290¢
Number of 20¢ coins in the end
= 1 u + 6 - 13
= 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 13 20-cent coins, the value of 20-cent coins is 290¢ more than the value of 10-cent coins. If another 290¢ 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 + 290
20 u - 10 u = 290 + 140
10 u = 430
1 u = 430 ÷ 10 = 43
Number of coins that Michael had in the end
= 1 u + 1 u - 7
= 2 u - 7
= (2 x 43) - 7
= 86 - 7
= 79
Answer(s): 79
