The auditorium had 1989 seats. There were 20% fewer $40-seats than $15-seats. 60% of the $15-seats and some $40-seats were sold. A total of $28585 was collected. How many seats were unsold?

	$40	$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 = 1989

1 u = 1989 ÷ 9 = 221

Total number of $15-seat tickets
= 5 u
= 5 x 221
= 1105

Number of $15-seat tickets sold
= 60% x 1105
= ⁶⁰₁₀₀ x 1105
= 663

Amount collected from $15-seat tickets sold
= 663 x 15
= $9945

Amount collected from $40-seat tickets sold
= 28585 - 9945
= $18640

Number of $40-seat tickets sold
= 18640 ÷ 40
= 466

Number of tickets sold
= 663 + 466
= 1129

Number of tickets left unsold
= 1989 - 1129
= 860

Answer(s): 860