25% of the people are performers for a concert and the rest are spectators. 70% of the spectators are children and there are 960 more child spectators than adult spectators. How many child spectators must leave so that 5% of the people are child spectators?

	Performers	Spectators
	1x10	3x10
		Adults	Children
		3x3	7x3
Before	10 u	9 u	21 u
Change			- ?
After	19x1 = 19 u		1x1 =  1 u

25% = ²⁵₁₀₀ = ¹₄ 

70% = ⁷⁰₁₀₀ = ⁷₁₀ 

5% = ⁵₁₀₀ = ¹₂₀

The total number of spectators at first is repeated.  Make the total number of spectators the same.  LCM of 3 and 10 is 30.

Number of more child spectators than adult spectators at first
= 21 u - 9 u
= 12 u

12 u = 960

1 u = 960 ÷ 12 = 80

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

Number of child spectators who must leave so that 5% of the people are child spectators
= 21 u - 1 u
= 20 u
= 20 x 80
= 1600

Answer(s): 1600