David had 5 times as many erasers as Fred at first. Then each of them bought an equal number of new erasers. In the end, Fred had 16 erasers and David had 3 times as many erasers as Fred. How many erasers did both of them buy altogether?
| |
David |
Fred |
Difference |
| Before |
5x1 =
5 u |
1x1 =
1 u |
4x1 =
4 u |
| Change |
+ ? |
+ ? |
|
| After |
3x2 =
6 u |
1x2 =
2 u |
2x2 =
4 u |
The difference in the number of erasers at first and in the end remains unchanged. Make the difference in the number of erasers at first and in the end the same. LCM of 4 and 2 is 4.
Number of erasers that Fred had in the end = 2 u
2 u = 16
1 u = 16 ÷ 2 = 8
Number of erasers that David bought
= 6 u - 5 u
= 1 u
Number of erasers that both of them bought altogether
= 2 x 1 u
= 2 u
= 2 x 8
= 16
Answer(s): 16
