There are 25% more brown marbles than grey marbles in a bag. After Tommy removed 20% of the brown marbles and increased the number of grey marbles by 20%, there are now 56 fewer brown marbles than grey marbles. Find the number of grey marbles at first.

	Brown	Grey
Before	5 u	4 u
Change	- 1 u	+ 0.8 u
After	4 u	4.8 u

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of brown marbles that Tommy removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

Number of grey marbles that Tommy increased 
= 20% x 4 u
= ²⁰₁₀₀  x 4 u
= 0.8 u

Number of brown marbles in the end
= 5 u - 1 u
= 4 u

Number of grey marbles in the end
= 4 u + 0.8 u
= 4.8 u

Number of fewer brown marbles than grey marbles in the end
= 4.8 u - 4 u 
= 0.8 u 

0.8 u = 56

1 u = 56 ÷ 0.8 = 70

Number of grey marbles at first
= 4 u
= 4 x 70
= 280

Answer(s): 280