The number of ten-cent coins in a bag was
14 the number of twenty-cent coins. David took out 18 twenty-cent coins and exchanged them for ten-cent coins. Then he put the money back into the bag. The number of twenty-cent coins became
25 the number of ten-cent coins. How much money was there in the bag?
|
Make u the same (1)x4 = (3) |
10-cent (1) |
20-cent (2) |
Before |
4 u |
1 u |
4 u |
Change |
+ 144 |
+ 36 |
- 18 |
After |
20 p |
5 p |
2 p |
Value of 20-cent coins to be exchanged to 10-cent coins
= 18 x 20
= 360
Number of 10-cent coins to be exchanged from the 20-cent coins
= 360 ÷ 10
= 36
(3) = (2)
20 p - 144 = 2 p + 18
20 p - 2 p = 18 + 144
18 p = 162
1 p = 162 ÷ 18 = 9
Number of 10-cent coins in the end
= 5 p
= 5 p x 9
= 45
Value of 10-cent coins in the end
= 45 x 10
= 450¢
Number of 20-cent coins in the end
= 2 p
= 2 x 9
= 18
Value of 20-cent coins in the end
= 18 x 20
= 360¢
Total value of coins
= 450 + 360
= 810¢
$1 = 100¢
810¢ = $8.10
Answer(s): $8.10