40% of the people are performers for a concert and the rest are spectators. 60% of the spectators are children and there are 120 more child spectators than adult spectators. How many child spectators must leave so that 20% of the people are child spectators?

	Performers	Spectators
	2x5	3x5
		Adults	Children
		2x3	3x3
Before	10 u	6 u	9 u
Change			- ?
After	4x4 = 16 u		1x4 =  4 u

40% = ⁴⁰₁₀₀ = ²₅ 

60% = ⁶⁰₁₀₀ = ³₅ 

20% = ²⁰₁₀₀ = ¹₅

The total number of spectators at first is repeated.  Make the total number of spectators the same.  LCM of 3 and 5 is 15.

Number of more child spectators than adult spectators at first
= 9 u - 6 u
= 3 u

3 u = 120

1 u = 120 ÷ 3 = 40

If some child spectators leave, the total number of adult spectators and performers remains unchanged.  

Number of child spectators who must leave so that 20% of the people are child spectators
= 9 u - 4 u
= 5 u
= 5 x 40
= 200

Answer(s): 200