The opera house had 1435 seats. There were 25% fewer $25-seats than $15-seats. 75% of the $15-seats and some $25-seats were sold. A total of $21700 was collected. How many seats were unsold?

	$25	$15	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 = 1435

1 u = 1435 ÷ 7 = 205

Total number of $15-seat tickets
= 4 u
= 4 x 205
= 820

Number of $15-seat tickets sold
= 75% x 820
= ⁷⁵₁₀₀ x 820
= 615

Amount collected from $15-seat tickets sold
= 615 x 15
= $9225

Amount collected from $25-seat tickets sold
= 21700 - 9225
= $12475

Number of $25-seat tickets sold
= 12475 ÷ 25
= 499

Number of tickets sold
= 615 + 499
= 1114

Number of tickets left unsold
= 1435 - 1114
= 321

Answer(s): 321