Luis had 6 times as many pens as Billy at first. Then each of them bought an equal number of new pens. In the end, Billy had 40 pens and Luis had 5 times as many pens as Billy. How many pens did both of them buy altogether?
| |
Luis |
Billy |
Difference |
| Before |
6x4 =
24 u |
1x4 =
4 u |
5x4 =
20 u |
| Change |
+ ? |
+ ? |
|
| After |
5x5 =
25 u |
1x5 =
5 u |
4x5 =
20 u |
The difference in the number of pens at first and in the end remains unchanged. Make the difference in the number of pens at first and in the end the same. LCM of 5 and 4 is 20.
Number of pens that Billy had in the end = 5 u
5 u = 40
1 u = 40 ÷ 5 = 8
Number of pens that Luis bought
= 25 u - 24 u
= 1 u
Number of pens that both of them bought altogether
= 2 x 1 u
= 2 u
= 2 x 8
= 16
Answer(s): 16
