Last week, David had a total of 135 red and grey pens. Two weeks later, he sold
23 of all the red pens and bought another 25 grey pens. Now he has the same number of red and grey pens. How many pens does he have in the end?
| |
Red |
Grey |
Total |
| Before |
3 u |
1 u - 25 |
4 u - 25 |
| Change |
- 2 u |
+ 25 |
|
| After |
1 u |
1 u |
|
Comparing the red
and grey pens in the end |
1 |
1 |
|
Total number of pens at first
= 3 u + 1 u - 25
= 4 u - 25
4 u - 25 = 135
4 u = 135 + 25
4 u = 160
1 u = 160 ÷ 4 = 40
Number of pens that he has in the end
= 1 u + 1 u
= 2 u
= 2 x 40
= 80
Answer(s): 80
