There are 25% more pink marbles than brown marbles in a bag. After David removed 40% of the pink marbles and increased the number of brown marbles by 10%, there are now 84 fewer pink marbles than brown marbles. Find the number of brown marbles at first.

	Pink	Brown
Before	5 u	4 u
Change	- 2 u	+ 0.4 u
After	3 u	4.4 u

Number of pink marbles in percentage
= 100% + 25%
= 125%

125% = ¹²⁵₁₀₀ = ⁵₄

Number of pink marbles that David removed
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u 
= 2 u

Number of brown marbles that David increased 
= 10% x 4 u
= ¹⁰₁₀₀  x 4 u
= 0.4 u

Number of pink marbles in the end
= 5 u - 2 u
= 3 u

Number of brown marbles in the end
= 4 u + 0.4 u
= 4.4 u

Number of fewer pink marbles than brown marbles in the end
= 4.4 u - 3 u 
= 1.4 u 

1.4 u = 84

1 u = 84 ÷ 1.4 = 60

Number of brown marbles at first
= 4 u
= 4 x 60
= 240

Answer(s): 240