The auditorium had 2160 seats. There were 20% fewer $30-seats than $20-seats. 50% of the $20-seats and some $30-seats were sold. A total of $25410 was collected. How many seats were unsold?

	$30	$20	Total
Number	4 u	5 u	9 u

100% - 20% = 80%
⁸⁰₁₀₀ = ⁴₅

Total number of seats
= 4 u + 5 u
= 9 u

9 u = 2160

1 u = 2160 ÷ 9 = 240

Total number of $20-seat tickets
= 5 u
= 5 x 240
= 1200

Number of $20-seat tickets sold
= 50% x 1200
= ⁵⁰₁₀₀ x 1200
= 600

Amount collected from $20-seat tickets sold
= 600 x 20
= $12000

Amount collected from $30-seat tickets sold
= 25410 - 12000
= $13410

Number of $30-seat tickets sold
= 13410 ÷ 30
= 447

Number of tickets sold
= 600 + 447
= 1047

Number of tickets left unsold
= 2160 - 1047
= 1113

Answer(s): 1113