The opera house had 1778 seats. There were 25% fewer $40-seats than $20-seats. 75% of the $20-seats and some $40-seats were sold. A total of $30160 was collected. How many seats were unsold?

	$40	$20	Total
Number	3 u	4 u	7 u

100% - 25% = 75%
⁷⁵₁₀₀ = ³₄

Total number of seats
= 3 u + 4 u
= 7 u

7 u = 1778

1 u = 1778 ÷ 7 = 254

Total number of $20-seat tickets
= 4 u
= 4 x 254
= 1016

Number of $20-seat tickets sold
= 75% x 1016
= ⁷⁵₁₀₀ x 1016
= 762

Amount collected from $20-seat tickets sold
= 762 x 20
= $15240

Amount collected from $40-seat tickets sold
= 30160 - 15240
= $14920

Number of $40-seat tickets sold
= 14920 ÷ 40
= 373

Number of tickets sold
= 762 + 373
= 1135

Number of tickets left unsold
= 1778 - 1135
= 643

Answer(s): 643