10 days ago, Hazel had a total of 250 silver and black stickers. 40% of her stickers were black stickers. Today, her younger brother gave her some more stickers. As a result, her silver stickers increased by 10%. Now, 50% of her stickers are black stickers. How many black stickers did her younger brother give her?

	Black stickers	Silver stickers	Total  stickers
Before	2 u	3 u	250
Change	+ 1.3 u	+ 0.3 u
After	3.3 u	3.3 u
Comparing the silver stickers and black stickers in the end	1	1

40% = ⁴⁰₁₀₀ = ²₅

Black stickers : Silver stickers = 2 : 3

Increase in the number of silver stickers
= 10% x 3 u
= ¹⁰₁₀₀ x 3 u
= 0.3 u

50% = ⁵⁰₁₀₀ = ¹₂

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

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

5 u = 250

1 u = 250 ÷ 5 = 50

Number of black stickers that Hazel received from her younger brother
= 3.3 u - 2 u
= 1.3 u
= 1.3 x 50
= 65

Answer(s): 65