There are 25% more grey coins than brown coins in a bag. After Mark removed 40% of the grey coins and increased the number of brown coins by 35%, there are now 216 fewer grey coins than brown coins. Find the number of brown coins at first.

	Grey	Brown
Before	5 u	4 u
Change	- 2 u	+ 1.4 u
After	3 u	5.4 u

Number of grey coins in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of grey coins that Mark removed
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u 
= 2 u

Number of brown coins that Mark increased 
= 35% x 4 u
= ³⁵₁₀₀  x 4 u
= 1.4 u

Number of grey coins in the end
= 5 u - 2 u
= 3 u

Number of brown coins in the end
= 4 u + 1.4 u
= 5.4 u

Number of fewer grey coins than brown coins in the end
= 5.4 u - 3 u 
= 2.4 u 

2.4 u = 216

1 u = 216 ÷ 2.4 = 90

Number of brown coins at first
= 4 u
= 4 x 90
= 360

Answer(s): 360