The opera house had 1539 seats. There were 20% fewer $40-seats than $10-seats. 60% of the $10-seats and some $40-seats were sold. A total of $19050 was collected. How many seats were unsold?

	$40	$10	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 = 1539

1 u = 1539 ÷ 9 = 171

Total number of $10-seat tickets
= 5 u
= 5 x 171
= 855

Number of $10-seat tickets sold
= 60% x 855
= ⁶⁰₁₀₀ x 855
= 513

Amount collected from $10-seat tickets sold
= 513 x 10
= $5130

Amount collected from $40-seat tickets sold
= 19050 - 5130
= $13920

Number of $40-seat tickets sold
= 13920 ÷ 40
= 348

Number of tickets sold
= 513 + 348
= 861

Number of tickets left unsold
= 1539 - 861
= 678

Answer(s): 678