The auditorium had 2628 seats. There were 20% fewer $30-seats than $15-seats. 60% of the $15-seats and some $30-seats were sold. A total of $25020 was collected. How many seats were unsold?

	$30	$15	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 = 2628

1 u = 2628 ÷ 9 = 292

Total number of $15-seat tickets
= 5 u
= 5 x 292
= 1460

Number of $15-seat tickets sold
= 60% x 1460
= ⁶⁰₁₀₀ x 1460
= 876

Amount collected from $15-seat tickets sold
= 876 x 15
= $13140

Amount collected from $30-seat tickets sold
= 25020 - 13140
= $11880

Number of $30-seat tickets sold
= 11880 ÷ 30
= 396

Number of tickets sold
= 876 + 396
= 1272

Number of tickets left unsold
= 2628 - 1272
= 1356

Answer(s): 1356