20% of the people are performers for a concert and the rest are spectators. 70% of the spectators are children and there are 160 more child spectators than parent spectators. How many child spectators must leave so that 45% of the people are child spectators?

	Performers	Spectators
	1x5	4x5
		Parents	Children
		3x2	7x2
Before	5 u	6 u	14 u
Change			- ?
After	11x1 = 11 u		9x1 =  9 u

20% = ²⁰₁₀₀ = ¹₅ 

70% = ⁷⁰₁₀₀ = ⁷₁₀ 

45% = ⁴⁵₁₀₀ = ⁹₂₀

The total number of spectators at first is repeated.  Make the total number of spectators the same.  LCM of 4 and 10 is 20.

Number of more child spectators than parent spectators at first
= 14 u - 6 u
= 8 u

8 u = 160

1 u = 160 ÷ 8 = 20

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

Number of child spectators who must leave so that 45% of the people are child spectators
= 14 u - 9 u
= 5 u
= 5 x 20
= 100

Answer(s): 100