David had 50% more stickers than Jackson. Lilian had 20% fewer stickers than David. David and Jackson gave Lilian some stickers in the ratio of 4 : 5. As a result, Lilian had 25% more stickers than before. Given that Lilian had 200 more stickers than Jackson in the end, how many stickers did David give to Lilian?

David	Jackson	Lilian
3x5	2x5
5x3		4x3
15	10	12

100% + 50% = 150%
150% = ¹⁵⁰₁₀₀ = ³₂

David : Jackson = 3 : 2

100% - 20% = 80%
80% = ⁸⁰₁₀₀ = ⁴₅

David : Lilian = 5 : 4

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

	David	Jackson	Lilian
Before	15x3 =  45 u	10x3 = 30 u	12x3 = 36 u
Change			+ 3x3 = + 9 u
Comparing the changes in the number of stickers	- 4x1 = - 4 u	- 5x1 = - 5 u	+ 9x1 = + 9 u
After	41 u	25 u	15x3 = 45 u

25% x 12 
= ²⁵₁₀₀ x 12 
= 3 

The total number of stickers that David and Jackson gave to Lilian is repeated.  Make the total number of stickers that David and Jackson gave to Lilian the same.  LCM of 9 and 3 is 9.

Number of stickers that Lilian had more than Jackson 
= 45 u - 25 u
= 20 u

20 u = 200

1 u = 200 ÷ 20 = 10

Number of stickers that David gave to Lilian
= 4 u
= 4 x 10
= 40

Answer(s): 40