At a concert hall, each adult ticket cost $27 and each child ticket cost $9. On Monday, the number of adult tickets sold was 142 less than the number of child tickets. On Tuesday, the number of adult tickets sold decreased by 25% while the number of child tickets sold increased by 50%. If a total of 1338 tickets were sold on Tuesday, how much money was collected on Monday?

	Adult tickets	Child tickets	Total tickets
Before	1 u	1 u + 142	2 u + 142
Change	- 0.25 u	+ 0.5 u + 71
After	0.75 u	1.5 u + 213	2.25 u + 213

25% x 1 u = ²⁵₁₀₀ x 1 u = 0.25 u 
50% x 1 u = ⁵⁰₁₀₀ x 1 u = 0.5 u
50% x 142 = ⁵⁰₁₀₀ x 142 = 71

Number of tickets sold on Tuesday
= 0.75 u + 1.5 u + 213
= 2.25 u + 213

2.25 u + 213 = 1338
2.25 u = 1338 - 213
2.25 u = 1125

1 u = 1125 ÷ 2.25 = 500

Amount collected from adult tickets on Monday
= 1 u x 27
= 500 x 27
= $13500

Amount collected from child tickets on Monday
= 9(1 u + 142)
= 9(500 + 142)
= 9 x 642
= $5778

Total amount collected on Monday
= 13500 + 5778
= $19278

Answer(s):$19278