The number of five-cent coins in a coin box was
15 the number of twenty-cent coins. Sean took out 20 twenty-cent coins and exchanged them for five-cent coins. Then he put the money back into the coin box. The number of twenty-cent coins became
58 the number of five-cent coins. How much money was there in the coin box?
|
Make u the same (1)x5 = (3) |
5-cent (1) |
20-cent (2) |
Before |
5 u |
1 u |
5 u |
Change |
+ 400 |
+ 80 |
- 20 |
After |
40 p |
8 p |
5 p |
Value of 20-cent coins to be exchanged to 5-cent coins
= 20 x 20
= 400
Number of 5-cent coins to be exchanged from the 20-cent coins
= 400 ÷ 5
= 80
(3) = (2)
40 p - 400 = 5 p + 20
40 p - 5 p = 20 + 400
35 p = 420
1 p = 420 ÷ 35 = 12
Number of 5-cent coins in the end
= 8 p
= 8 p x 12
= 96
Value of 5-cent coins in the end
= 96 x 5
= 480¢
Number of 20-cent coins in the end
= 5 p
= 5 x 12
= 60
Value of 20-cent coins in the end
= 60 x 20
= 1200¢
Total value of coins
= 480 + 1200
= 1680¢
$1 = 100¢
1680¢ = $16.80
Answer(s): $16.80