There are 25% more yellow marbles than gold marbles in a bag. After Ian removed 20% of the yellow marbles and increased the number of gold marbles by 35%, there are now 42 fewer yellow marbles than gold marbles. Find the number of gold marbles at first.

	Yellow	Gold
Before	5 u	4 u
Change	- 1 u	+ 1.4 u
After	4 u	5.4 u

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

125% = ¹²⁵₁₀₀ = ⁵₄

Number of yellow marbles that Ian removed
= 20% x 5 u
= ²⁰₁₀₀ x 5 u 
= 1 u

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

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

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

Number of fewer yellow marbles than gold marbles in the end
= 5.4 u - 4 u 
= 1.4 u 

1.4 u = 42

1 u = 42 ÷ 1.4 = 30

Number of gold marbles at first
= 4 u
= 4 x 30
= 120

Answer(s): 120