Tim had 3 times as many purple pens as black pens. After giving away 4 purple pens and buying another 16 black pens, he had an equal number of purple and black pens. How many purple pens did Tim have at first?
| |
Purple pens |
Black pens |
| Before |
3 u |
1 u |
| Change |
- 4 |
+ 16 |
| After |
3 u - 4 |
1 u + 16 |
The number of purple and black pens is the same in the end.
3 u - 4 = 1 u + 16
3 u - 1 u = 16 + 4
2 u = 4 + 16
2 u = 20
1 u = 20 ÷ 2 = 10
Number of purple pens that Tim had at first
= 3 u
= 3 x 10
= 30
Answer(s): 30
