There are 25% more black marbles than purple marbles in a bag. After Lee removed 40% of the black marbles and increased the number of purple marbles by 10%, there are now 28 fewer black marbles than purple marbles. Find the number of purple marbles at first.

	Black	Purple
Before	5 u	4 u
Change	- 2 u	+ 0.4 u
After	3 u	4.4 u

Number of black marbles in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of black marbles that Lee removed
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u 
= 2 u

Number of purple marbles that Lee increased 
= 10% x 4 u
= ¹⁰₁₀₀  x 4 u
= 0.4 u

Number of black marbles in the end
= 5 u - 2 u
= 3 u

Number of purple marbles in the end
= 4 u + 0.4 u
= 4.4 u

Number of fewer black marbles than purple marbles in the end
= 4.4 u - 3 u 
= 1.4 u 

1.4 u = 28

1 u = 28 ÷ 1.4 = 20

Number of purple marbles at first
= 4 u
= 4 x 20
= 80

Answer(s): 80