Oscar, Gabriel and Simon have some erasers. The ratios of their erasers are as follows:

Oscar : (Oscar + Gabriel + Simon) = 1 : 4
Gabriel : (Oscar + Simon) = 1 : 4

Simon has 42 erasers more than Gabriel. In the end, Simon gives away all he has to Gabriel and Oscar so that both Gabriel and Oscar end up with the same number of erasers, how many erasers has Oscar received from Simon?

Gabriel	Simon	Oscar	Total
3x5		1x5	4x5
1x4	4x4		5x4
4 u	11 u	5 u	20 u

The total number of erasers is repeated.  Make the total number of erasers the same.  LCM of 4 and 5 is 20.

Number of erasers that Simon has more than Gabriel
= 11 u - 4 u
= 7 u

7 u = 42

1 u = 42 ÷ 7 = 6

	Gabriel	Simon	Oscar
Before	4 u	11 u	5 u
Change	+ 6 u	- 11 u	+ 5 u
After	10 u	0 u	10 u

Number of erasers that Oscar has received from Simon
= 10 u - 5 u 
= 5 u
= 5 x 6
= 30

Answer(s): 30