The number of twenty-cent coins in a bag was 100% more than the number of ten-cent coins. 11 twenty-cent coins were taken out and exchanged for ten-cent coins. The number of 20-cent coins became
47 less than the number of 10-cent coins. How much money is there in the bag?
|
Twenty-cent (1) |
Ten-cent (2) |
Make u the same (2)x2 = (3) |
Before |
2 u |
1 u |
2 u |
Change |
- 11 |
+ 22 |
+ 44 |
After |
3 p |
7 p |
14 p |
100 + 100100=
200100 =
21 At first
Twenty-cent coins : Ten-cent coins
2 : 1
1 -
47 =
37 In the end
Twenty-cent coins : Ten-cent coins
3 : 7
Total value of 20-cent coins to be taken out
= 11 x 20
= 220¢
Total number of 10-cent coins to be exchanged for
= 220 ÷ 10
= 22
Notice that the number of 10-cent coins is 1 u at first. So, instead of making p the same, we can make u the same so we create one extra equation instead of 2.
2 u - 11 = 3 p
2 u = 3 p + 11 --- (1)
1 u + 22 = 7 p --- (2)
(2)x2
2 u + 44 = 14 p
2 u = 14 p - 44 --- (3)
(3) = (1)
14 p - 44 = 3 p + 11
14 p - 3 p = 11 + 44
11 p = 55
1 p = 55 ÷ 11 = 5
The total value of the coins at first and in the end remains unchanged.
Total value of twenty-cent coins in the end
= 3 p x 20
= 3 x 5 x 20
= 300¢
Total value of ten-cent coins in the end
= 7 p x 10
= 7 x 5 x 10
= 350¢
Total value of the coins
= 300 + 350
= 650¢
= $6.50
Answer(s): $6.50