5 days ago, Risa had a total of 100 brown and yellow stickers. 30% of her stickers were yellow stickers. Today, her younger sister gave her some more stickers. As a result, her brown stickers increased by 10%. Now, 50% of her stickers are yellow stickers. How many yellow stickers did her younger sister give her?

	Yellow stickers	Brown stickers	Total  stickers
Before	3 u	7 u	100
Change	+ 4.7 u	+ 0.7 u
After	7.7 u	7.7 u
Comparing the brown stickers and yellow stickers in the end	1	1

30% = ³⁰₁₀₀ = ³₁₀

Yellow stickers : Brown stickers = 3 : 7

Increase in the number of brown stickers
= 10% x 7 u
= ¹⁰₁₀₀ x 7 u
= 0.7 u

50% = ⁵⁰₁₀₀ = ¹₂

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

Number of stickers at first
= 7 u + 3 u
= 10 u 

10 u = 100

1 u = 100 ÷ 10 = 10

Number of yellow stickers that Risa received from her younger sister
= 7.7 u - 3 u
= 4.7 u
= 4.7 x 10
= 47

Answer(s): 47