There are 25% more yellow marbles than purple marbles in a bag. After Bobby removed 20% of the yellow marbles and increased the number of purple marbles by 10%, there are now 28 fewer yellow marbles than purple marbles. Find the number of purple marbles at first.

	Yellow	Purple
Before	5 u	4 u
Change	- 1 u	+ 0.4 u
After	4 u	4.4 u

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of yellow marbles that Bobby removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

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

Number of yellow marbles in the end
= 5 u - 1 u
= 4 u

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

Number of fewer yellow marbles than purple marbles in the end
= 4.4 u - 4 u 
= 0.4 u 

0.4 u = 28

1 u = 28 ÷ 0.4 = 70

Number of purple marbles at first
= 4 u
= 4 x 70
= 280

Answer(s): 280