There are 25% more yellow pens than blue pens in a bag. After Luis removed 20% of the yellow pens and increased the number of blue pens by 10%, there are now 16 fewer yellow pens than blue pens. Find the number of blue pens at first.

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

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of yellow pens that Luis removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

Number of blue pens that Luis increased 
= 10% x 4 u
= ¹⁰₁₀₀  x 4 u
= 0.4 u

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

Number of blue pens in the end
= 4 u + 0.4 u
= 4.4 u

Number of fewer yellow pens than blue pens in the end
= 4.4 u - 4 u 
= 0.4 u 

0.4 u = 16

1 u = 16 ÷ 0.4 = 40

Number of blue pens at first
= 4 u
= 4 x 40
= 160

Answer(s): 160