Mark has 4 more 20-cent coins than 10-cent coins. After he used 10 of his 20-cent coins, the total value of 20-cent coins is $1.70 more than the total value of 10-cent coins. How many coins did he have in the end?
|
20¢ |
10¢ |
Before |
1 u + 4 |
1 u |
Change |
- 10 |
|
After |
1 u - 6 |
1 u |
|
20¢ |
10¢ |
Number |
1 u - 6 |
1 u |
Value |
20 |
10 |
Total value |
20 u - 120 |
10 u |
$1 = 100¢
$1.70 = 170¢
Number of 20¢ coins in the end
= 1 u + 4 - 10
= 1 u - 6
Total value of 20¢ coins in the end
= 20 x (1 u - 6)
= 20 u - 120
Total value of 10¢ coins in the end
= 10 x 1 u
= 10 u
After using 10 20-cent coins, the value of 20-cent coins is 170¢ more than the value of 10-cent coins. If another 170¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.
20 u - 120 = 10 u + 170
20 u - 10 u = 170 + 120
10 u = 290
1 u = 290 ÷ 10 = 29
Number of coins that Mark had in the end
= 1 u + 1 u - 6
= 2 u - 6
= (2 x 29) - 6
= 58 - 6
= 52
Answer(s): 52