Eric had 6 times as many erasers as David at first. Then each of them bought an equal number of new erasers. In the end, David had 45 erasers and Eric had 5 times as many erasers as David. How many erasers did both of them buy altogether?
| |
Eric |
David |
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 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 5 and 4 is 20.
Number of erasers that David had in the end = 5 u
5 u = 45
1 u = 45 ÷ 5 = 9
Number of erasers that Eric bought
= 25 u - 24 u
= 1 u
Number of erasers that both of them bought altogether
= 2 x 1 u
= 2 u
= 2 x 9
= 18
Answer(s): 18
