The auditorium had 2124 seats. There were 20% fewer $30-seats than $20-seats. 60% of the $20-seats and some $30-seats were sold. A total of $28950 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 = 2124

1 u = 2124 ÷ 9 = 236

Total number of $20-seat tickets
= 5 u
= 5 x 236
= 1180

Number of $20-seat tickets sold
= 60% x 1180
= ⁶⁰₁₀₀ x 1180
= 708

Amount collected from $20-seat tickets sold
= 708 x 20
= $14160

Amount collected from $30-seat tickets sold
= 28950 - 14160
= $14790

Number of $30-seat tickets sold
= 14790 ÷ 30
= 493

Number of tickets sold
= 708 + 493
= 1201

Number of tickets left unsold
= 2124 - 1201
= 923

Answer(s): 923