14 days ago, Tammy had a total of 225 purple and yellow marbles. 20% of her marbles were yellow marbles. Today, her younger sister gave her some more marbles. As a result, her purple marbles increased by 40%. Now, 50% of her marbles are yellow marbles. How many yellow marbles did her younger sister give her?

	Yellow marbles	Purple marbles	Total  marbles
Before	1 u	4 u	225
Change	+ 4.6 u	+ 1.6 u
After	5.6 u	5.6 u
Comparing the purple marbles and yellow marbles in the end	1	1

20% = ²⁰₁₀₀ = ¹₅

Yellow marbles : Purple marbles = 1 : 4

Increase in the number of purple marbles
= 40% x 4 u
= ⁴⁰₁₀₀ x 4 u
= 1.6 u

50% = ⁵⁰₁₀₀ = ¹₂

In the end
Yellow marbles : Purple marbles = 1 : 1

Number of marbles at first
= 4 u + 1 u
= 5 u 

5 u = 225

1 u = 225 ÷ 5 = 45

Number of yellow marbles that Tammy received from her younger sister
= 5.6 u - 1 u
= 4.6 u
= 4.6 x 45
= 207

Answer(s): 207