The auditorium had 1463 seats. There were 25% fewer $30-seats than $15-seats. 50% of the $15-seats and some $30-seats were sold. A total of $20370 was collected. How many seats were unsold?

	$30	$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 = 1463

1 u = 1463 ÷ 7 = 209

Total number of $15-seat tickets
= 4 u
= 4 x 209
= 836

Number of $15-seat tickets sold
= 50% x 836
= ⁵⁰₁₀₀ x 836
= 418

Amount collected from $15-seat tickets sold
= 418 x 15
= $6270

Amount collected from $30-seat tickets sold
= 20370 - 6270
= $14100

Number of $30-seat tickets sold
= 14100 ÷ 30
= 470

Number of tickets sold
= 418 + 470
= 888

Number of tickets left unsold
= 1463 - 888
= 575

Answer(s): 575