There are 25% more grey marbles than gold marbles in a bag. After Ben removed 40% of the grey marbles and increased the number of gold marbles by 35%, there are now 168 fewer grey marbles than gold marbles. Find the number of gold marbles at first.

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

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of grey marbles that Ben removed
= 40% x 5 u
= ⁴⁰₁₀₀ x 5 u 
= 2 u

Number of gold marbles that Ben increased 
= 35% x 4 u
= ³⁵₁₀₀  x 4 u
= 1.4 u

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

Number of gold marbles in the end
= 4 u + 1.4 u
= 5.4 u

Number of fewer grey marbles than gold marbles in the end
= 5.4 u - 3 u 
= 2.4 u 

2.4 u = 168

1 u = 168 ÷ 2.4 = 70

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

Answer(s): 280