There are 25% more white cards than gold cards in a bag. After Pierre removed 40% of the white cards and increased the number of gold cards by 20%, there are now 36 fewer white cards than gold cards. Find the number of gold cards at first.

	White	Gold
Before	5 u	4 u
Change	- 2 u	+ 0.8 u
After	3 u	4.8 u

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of white cards that Pierre removed
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u 
= 2 u

Number of gold cards that Pierre increased 
= 20% x 4 u
= ²⁰₁₀₀  x 4 u
= 0.8 u

Number of white cards in the end
= 5 u - 2 u
= 3 u

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

Number of fewer white cards than gold cards in the end
= 4.8 u - 3 u 
= 1.8 u 

1.8 u = 36

1 u = 36 ÷ 1.8 = 20

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

Answer(s): 80