There are 25% more green cards than black cards in a bag. After Ryan removed 20% of the green cards and increased the number of black cards by 30%, there are now 144 fewer green cards than black cards. Find the number of black cards at first.

	Green	Black
Before	5 u	4 u
Change	- 1 u	+ 1.2 u
After	4 u	5.2 u

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

125% = ¹²⁵₁₀₀ = ⁵₄

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

Number of black cards that Ryan increased 
= 30% x 4 u
= ³⁰₁₀₀  x 4 u
= 1.2 u

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

Number of black cards in the end
= 4 u + 1.2 u
= 5.2 u

Number of fewer green cards than black cards in the end
= 5.2 u - 4 u 
= 1.2 u 

1.2 u = 144

1 u = 144 ÷ 1.2 = 120

Number of black cards at first
= 4 u
= 4 x 120
= 480

Answer(s): 480