The ratio of the number of red erasers to green erasers is 7 : 5. After Andy gives away 10 red erasers and buys another 20 green erasers, there is equal number of red erasers and green erasers. How many erasers does Andy have now?
| |
Red |
Green |
| Before |
7 u |
5 u |
| Change |
- 10 |
+ 20 |
| After |
7 u - 10 |
5 u + 20 |
The number of red erasers and green erasers in the end is the same.
7 u - 10 = 5 u + 20
7 u - 5 u = 20 + 10
2 u = 30
1 u = 30 ÷ 2 = 15
Number of erasers that Andy has now
= 7 u - 10 + 5 u + 20
= 7 u + 5 u - 10 + 20
= 12 u + 10
= 12 x 15 + 10
= 180 + 10
= 190
Answer(s): 190
