The auditorium had 1584 seats. There were 20% fewer $45-seats than $15-seats. 60% of the $15-seats and some $45-seats were sold. A total of $25200 was collected. How many seats were unsold?

	$45	$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 = 1584

1 u = 1584 ÷ 9 = 176

Total number of $15-seat tickets
= 5 u
= 5 x 176
= 880

Number of $15-seat tickets sold
= 60% x 880
= ⁶⁰₁₀₀ x 880
= 528

Amount collected from $15-seat tickets sold
= 528 x 15
= $7920

Amount collected from $45-seat tickets sold
= 25200 - 7920
= $17280

Number of $45-seat tickets sold
= 17280 ÷ 45
= 384

Number of tickets sold
= 528 + 384
= 912

Number of tickets left unsold
= 1584 - 912
= 672

Answer(s): 672