A coin bank contains some five-cent and fifty-cent coins in the ratio of 5 : 4.
When 9 fifty-cent coins are taken out and
exchanged with some five-cent coins of the same value,
the ratio became 10 : 7.
Find the sum of money in the coin box in dollars.
|
Make p the same. (1) x 7 = (3) |
(1) 5-cent |
(2) 50-cent |
Make p the same. (2) x 10 = (4) |
Before |
35 u |
5 u |
4 u |
40 u |
Change |
+ 630 |
+ 90 |
- 9 |
- 90 |
After |
70 p |
10 p |
7 p |
70 p |
Value of 9 fifty-cent coins
= 9 x 50
= 450¢
Number of five-cent coins to exchange for
= 450 ÷ 5
= 90
5 u + 90 = 10 p --- (1)
4 u - 9 = 7 p --- (2)
Make p the same.
(1)
x 7 35 u + 630 = 70 p --- (3)
(2)
x 10 40 u - 90 = 70 p --- (4)
(4) = (3)
40 u - 90 = 35 u + 630
40 u - 35 u = 630 + 90
5 u = 720
1 u = 720 ÷ 5 = 144
Value of five-cent coins
= 5 u x 5
= 5 x 144 x 5
= 3600¢
Value of fifty-cent coins
= 4 u x 50
= 4 x 144 x 50
= 28800¢
Total value of coins
= 3600 + 28800
= 32400¢
100¢ = $1
Sum of money in the coin box
= 32400¢
= $324
Answer(s): $324