The number of ten-cent coins in a bottle was
13 the number of twenty-cent coins. Brandon took out 21 twenty-cent coins and exchanged them for ten-cent coins. Then he put the money back into the bottle. The number of twenty-cent coins became
38 the number of ten-cent coins. How much money was there in the bottle?
|
Make u the same (1)x3 = (3) |
10-cent (1) |
20-cent (2) |
Before |
3 u |
1 u |
3 u |
Change |
+ 126 |
+ 42 |
- 21 |
After |
24 p |
8 p |
3 p |
Value of 20-cent coins to be exchanged to 10-cent coins
= 21 x 20
= 420
Number of 10-cent coins to be exchanged from the 20-cent coins
= 420 ÷ 10
= 42
(3) = (2)
24 p - 126 = 3 p + 21
24 p - 3 p = 21 + 126
21 p = 147
1 p = 147 ÷ 21 = 7
Number of 10-cent coins in the end
= 8 p
= 8 p x 7
= 56
Value of 10-cent coins in the end
= 56 x 10
= 560¢
Number of 20-cent coins in the end
= 3 p
= 3 x 7
= 21
Value of 20-cent coins in the end
= 21 x 20
= 420¢
Total value of coins
= 560 + 420
= 980¢
$1 = 100¢
980¢ = $9.80
Answer(s): $9.80