Luke had 4 times as many black files as grey files. After giving away 7 black files and buying another 14 grey files, he had an equal number of black and grey files. How many black files did Luke have at first?
| |
Black files |
Grey files |
| Before |
4 u |
1 u |
| Change |
- 7 |
+ 14 |
| After |
4 u - 7 |
1 u + 14 |
The number of black and grey files is the same in the end.
4 u - 7 = 1 u + 14
4 u - 1 u = 14 + 7
3 u = 7 + 14
3 u = 21
1 u = 21 ÷ 3 = 7
Number of black files that Luke had at first
= 4 u
= 4 x 7
= 28
Answer(s): 28
