Warren and Ivan shared some stamps in the ratio of 5 : 7. After both each gave away 15 stamps to their brother, the ratio of the number of stamps Warren had to the total number of stamps left was 1 : 3. How many stamps did the two boys have at first?

	Warren	Ivan	Difference
Before	5x1 = 5 u	7x1 = 7 u	2x1 = 2 u
Change	- 15	- 15
After	1x2 = 2 u	2x2 = 4 u	1x2 = 2 u

Number of stamps that Warren and Ivan each gave to their brother is the same.

The difference in the number of stamps at first and in the end between Warren and Ivan remains unchanged.  Make the difference in the number of stamps the same.  LCM of 2 and 1 is 2.

Number of stamps that Warren gave to their brother
= 5 u - 2 u
= 3 u

3 u = 15

1 u = 15 ÷ 3 = 5

Number of stamps that the two boys had at first
= 5 u + 7 u
= 12 u
= 12 x 5
= 60

Answer(s): 60