25% of the people are performers for a concert and the rest are spectators. 80% of the spectators are adults and there are 1530 less child spectators than adult spectators. How many adult spectators must join so that 84% of the people are adult spectators?

	Performers	Spectators
	1x5	3x5
		Children	Adults
		1x3	4x3
Before	5 u	3 u	12 u
Change			+ ?
After	4x2 = 8 u		21x2 =  42 u

25% = ²⁵₁₀₀ = ¹₄ 

80% = ⁸⁰₁₀₀ = ⁴₅ 

84% = ⁸⁴₁₀₀ = ²¹₂₅

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 less child spectators than adult spectators at first
= 12 u - 3 u
= 9 u

9 u = 1530

1 u = 1530 ÷ 9 = 170

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

Number of adult spectators who must join so that 84% of the people are adult spectators
= 42 u - 12 u
= 30 u
= 30 x 170
= 5100

Answer(s): 5100