The ratio of the number of green erasers to blue erasers is 7 : 2. After Bobby gives away 40 green erasers and buys another 50 blue erasers, there is equal number of green erasers and blue erasers. How many erasers does Bobby have now?
| |
Green |
Blue |
| Before |
7 u |
2 u |
| Change |
- 40 |
+ 50 |
| After |
7 u - 40 |
2 u + 50 |
The number of green erasers and blue erasers in the end is the same.
7 u - 40 = 2 u + 50
7 u - 2 u = 50 + 40
5 u = 90
1 u = 90 ÷ 5 = 18
Number of erasers that Bobby has now
= 7 u - 40 + 2 u + 50
= 7 u + 2 u - 40 + 50
= 9 u + 10
= 9 x 18 + 10
= 162 + 10
= 172
Answer(s): 172
