The number of five-cent coins in a coin box was
13 the number of twenty-cent coins. Nick took out 16 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
25 the number of five-cent coins. How much money was there in the coin box?
|
Make u the same (1)x3 = (3) |
5-cent (1) |
20-cent (2) |
Before |
3 u |
1 u |
3 u |
Change |
+ 192 |
+ 64 |
- 16 |
After |
15 p |
5 p |
2 p |
Value of 20-cent coins to be exchanged to 5-cent coins
= 16 x 20
= 320
Number of 5-cent coins to be exchanged from the 20-cent coins
= 320 ÷ 5
= 64
(3) = (2)
15 p - 192 = 2 p + 16
15 p - 2 p = 16 + 192
13 p = 208
1 p = 208 ÷ 13 = 16
Number of 5-cent coins in the end
= 5 p
= 5 p x 16
= 80
Value of 5-cent coins in the end
= 80 x 5
= 400¢
Number of 20-cent coins in the end
= 2 p
= 2 x 16
= 32
Value of 20-cent coins in the end
= 32 x 20
= 640¢
Total value of coins
= 400 + 640
= 1040¢
$1 = 100¢
1040¢ = $10.40
Answer(s): $10.40