Flynn, Ivan and Riordan have some marbles. The ratios of their marbles are as follows:

Flynn : (Flynn + Ivan + Riordan) = 3 : 7
Ivan : (Flynn + Riordan) = 1 : 3

Riordan has 4 marbles more than Ivan. In the end, Riordan gives away all he has to Ivan and Flynn so that both Ivan and Flynn end up with the same number of marbles, how many marbles has Ivan received from Riordan?

Ivan	Riordan	Flynn	Total
4x4		3x4	7x4
1x7	3x7		4x7
7 u	9 u	12 u	28 u

The total number of marbles is repeated.  Make the total number of marbles the same.  LCM of 7 and 4 is 28.

Number of marbles that Riordan has more than Ivan
= 9 u - 7 u
= 2 u

2 u = 4

1 u = 4 ÷ 2 = 2

	Ivan	Riordan	Flynn
Before	7 u	9 u	12 u
Change	+ 7 u	- 9 u	+ 2 u
After	14 u	0 u	14 u

Number of marbles that Ivan has received from Riordan
= 14 u - 7 u 
= 7 u
= 7 x 2
= 14

Answer(s): 14