The ratio of the number of red erasers to green erasers is 7 : 2. After Bobby gives away 10 red erasers and buys another 90 green erasers, there is equal number of red erasers and green erasers. How many erasers does Bobby have now?
| |
Red |
Green |
| Before |
7 u |
2 u |
| Change |
- 10 |
+ 90 |
| After |
7 u - 10 |
2 u + 90 |
The number of red erasers and green erasers in the end is the same.
7 u - 10 = 2 u + 90
7 u - 2 u = 90 + 10
5 u = 100
1 u = 100 ÷ 5 = 20
Number of erasers that Bobby has now
= 7 u - 10 + 2 u + 90
= 7 u + 2 u - 10 + 90
= 9 u + 80
= 9 x 20 + 80
= 180 + 80
= 260
Answer(s): 260
