The ratio of the number of blue erasers to red erasers is 9 : 5. After Oliver gives away 70 blue erasers and buys another 90 red erasers, there is equal number of blue erasers and red erasers. How many erasers does Oliver have now?
| |
Blue |
Red |
| Before |
9 u |
5 u |
| Change |
- 70 |
+ 90 |
| After |
9 u - 70 |
5 u + 90 |
The number of blue erasers and red erasers in the end is the same.
9 u - 70 = 5 u + 90
9 u - 5 u = 90 + 70
4 u = 160
1 u = 160 ÷ 4 = 40
Number of erasers that Oliver has now
= 9 u - 70 + 5 u + 90
= 9 u + 5 u - 70 + 90
= 14 u + 20
= 14 x 40 + 20
= 560 + 20
= 580
Answer(s): 580
