Robert had 50% more stickers than Gavin. Mason had 20% fewer stickers than Robert. Robert and Gavin gave Mason some stickers in the ratio of 1 : 3. As a result, Mason had 25% more stickers than before. Given that Mason had 261 more stickers than Gavin in the end, how many stickers did Robert give to Mason?

Robert	Gavin	Mason
3x5	2x5
5x3		4x3
15	10	12

100% + 50% = 150%
150% = ¹⁵⁰₁₀₀ = ³₂

Robert : Gavin = 3 : 2

100% - 20% = 80%
80% = ⁸⁰₁₀₀ = ⁴₅

Robert : Mason = 5 : 4

The number of stickers that Robert had at first is repeated. Make the number of stickers that Robert had at first the same.  LCM of 3 and 5 is 15.

	Robert	Gavin	Mason
Before	15x4 =  60 u	10x4 = 40 u	12x4 = 48 u
Change			+ 3x4 = + 12 u
Comparing the changes in the number of stickers	- 1x3 = - 3 u	- 3x3 = - 9 u	+ 4x3 = + 12 u
After	57 u	31 u	15x4 = 60 u

25% x 12 
= ²⁵₁₀₀ x 12 
= 3 

The total number of stickers that Robert and Gavin gave to Mason is repeated.  Make the total number of stickers that Robert and Gavin gave to Mason the same.  LCM of 4 and 3 is 12.

Number of stickers that Mason had more than Gavin 
= 60 u - 31 u
= 29 u

29 u = 261

1 u = 261 ÷ 29 = 9

Number of stickers that Robert gave to Mason
= 3 u
= 3 x 9
= 27

Answer(s): 27