Oscar and Cody shared some erasers in the ratio of 3 : 7. After both each gave away 25 erasers to their cousin, the ratio of the number of erasers Oscar had to the total number of erasers left was 1 : 5. How many erasers did the two boys have at first?

	Oscar	Cody	Difference
Before	3x3 = 9 u	7x3 = 21 u	4x3 = 12 u
Change	- 25	- 25
After	1x4 = 4 u	4x4 = 16 u	3x4 = 12 u

Number of erasers that Oscar and Cody each gave to their cousin is the same.

The difference in the number of erasers at first and in the end between Oscar and Cody remains unchanged.  Make the difference in the number of erasers the same.  LCM of 4 and 3 is 12.

Number of erasers that Oscar gave to their cousin
= 9 u - 4 u
= 5 u

5 u = 25

1 u = 25 ÷ 5 = 5

Number of erasers that the two boys had at first
= 9 u + 21 u
= 30 u
= 30 x 5
= 150

Answer(s): 150