15 days ago, Fiona had a total of 200 black and brown stickers. 40% of her stickers were brown stickers. Today, her younger sister gave her some more stickers. As a result, her black stickers increased by 20%. Now, 50% of her stickers are brown stickers. How many brown stickers did her younger sister give her?

	Brown stickers	Black stickers	Total  stickers
Before	2 u	3 u	200
Change	+ 1.6 u	+ 0.6 u
After	3.6 u	3.6 u
Comparing the black stickers and brown stickers in the end	1	1

40% = ⁴⁰₁₀₀ = ²₅

Brown stickers : Black stickers = 2 : 3

Increase in the number of black stickers
= 20% x 3 u
= ²⁰₁₀₀ x 3 u
= 0.6 u

50% = ⁵⁰₁₀₀ = ¹₂

In the end
Brown stickers : Black stickers = 1 : 1

Number of stickers at first
= 3 u + 2 u
= 5 u 

5 u = 200

1 u = 200 ÷ 5 = 40

Number of brown stickers that Fiona received from her younger sister
= 3.6 u - 2 u
= 1.6 u
= 1.6 x 40
= 64

Answer(s): 64