Billy has 2 more 20-cent coins than 10-cent coins. After he used 6 of his 20-cent coins, the total value of 20-cent coins is $3.30 more than the total value of 10-cent coins. How many coins did he have at first?
|
20¢ |
10¢ |
Before |
1 u + 2 |
1 u |
Change |
- 6 |
|
After |
1 u - 4 |
1 u |
|
20¢ |
10¢ |
Number |
1 u - 4 |
1 u |
Value |
20 |
10 |
Total value |
20 u - 80 |
10 u |
$1 = 100¢
$3.30 = 330¢
Number of 20¢ coins in the end
= 1 u + 2 - 6
= 1 u - 4
Total value of 20¢ coins in the end
= 20 x (1 u - 4)
= 20 u - 80
Total value of 10¢ coins in the end
= 10 x 1 u
= 10 u
After using 6 20-cent coins, the value of 20-cent coins is 330¢ more than the value of 10-cent coins. If another 330¢ is added to the 10-cent coins, the total value of 20-cent coins and 10-cent coins will be the same.
20 u - 80 = 10 u + 330
20 u - 10 u = 330 + 80
10 u = 410
1 u = 410 ÷ 10 = 41
Number of coins that Billy had at first
= 1 u + 1 u + 2
= 2 u + 2
= (2 x 41) + 2
= 82 + 2
= 84
Answer(s): 84