The ratio of the number of red pens to blue pens is 3 : 1. After Mark gives away 30 red pens and buys another 40 blue pens, there is equal number of red pens and blue pens. How many pens does Mark have now?
| |
Red |
Blue |
| Before |
3 u |
1 u |
| Change |
- 30 |
+ 40 |
| After |
3 u - 30 |
1 u + 40 |
The number of red pens and blue pens in the end is the same.
3 u - 30 = 1 u + 40
3 u - 1 u = 40 + 30
2 u = 70
1 u = 70 ÷ 2 = 35
Number of pens that Mark has now
= 3 u - 30 + 1 u + 40
= 3 u + 1 u - 30 + 40
= 4 u + 10
= 4 x 35 + 10
= 140 + 10
= 150
Answer(s): 150
