Peter had 4 times as many yellow pens as white pens. After giving away 10 yellow pens and buying another 5 white pens, he had an equal number of yellow and white pens. How many yellow pens did Peter have at first?
| |
Yellow pens |
White pens |
| Before |
4 u |
1 u |
| Change |
- 10 |
+ 5 |
| After |
4 u - 10 |
1 u + 5 |
The number of yellow and white pens is the same in the end.
4 u - 10 = 1 u + 5
4 u - 1 u = 5 + 10
3 u = 10 + 5
3 u = 15
1 u = 15 ÷ 3 = 5
Number of yellow pens that Peter had at first
= 4 u
= 4 x 5
= 20
Answer(s): 20
