There are 25% more blue buttons than red buttons in a bag. After Mark removed 20% of the blue buttons and increased the number of red buttons by 30%, there are now 84 fewer blue buttons than red buttons. Find the number of red buttons at first.

	Blue	Red
Before	5 u	4 u
Change	- 1 u	+ 1.2 u
After	4 u	5.2 u

Number of blue buttons in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of blue buttons that Mark removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

Number of red buttons that Mark increased 
= 30% x 4 u
= ³⁰₁₀₀  x 4 u
= 1.2 u

Number of blue buttons in the end
= 5 u - 1 u
= 4 u

Number of red buttons in the end
= 4 u + 1.2 u
= 5.2 u

Number of fewer blue buttons than red buttons in the end
= 5.2 u - 4 u 
= 1.2 u 

1.2 u = 84

1 u = 84 ÷ 1.2 = 70

Number of red buttons at first
= 4 u
= 4 x 70
= 280

Answer(s): 280