There are 25% more green cards than black cards in a bag. After George removed 20% of the green cards and increased the number of black cards by 20%, there are now 16 fewer green cards than black cards. Find the number of black cards at first.

	Green	Black
Before	5 u	4 u
Change	- 1 u	+ 0.8 u
After	4 u	4.8 u

Number of green cards in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of green cards that George removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

Number of black cards that George increased 
= 20% x 4 u
= ²⁰₁₀₀  x 4 u
= 0.8 u

Number of green cards in the end
= 5 u - 1 u
= 4 u

Number of black cards in the end
= 4 u + 0.8 u
= 4.8 u

Number of fewer green cards than black cards in the end
= 4.8 u - 4 u 
= 0.8 u 

0.8 u = 16

1 u = 16 ÷ 0.8 = 20

Number of black cards at first
= 4 u
= 4 x 20
= 80

Answer(s): 80