The auditorium had 1470 seats. There were 25% fewer $45-seats than $20-seats. 80% of the $20-seats and some $45-seats were sold. A total of $34905 was collected. How many seats were unsold?

	$45	$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 = 1470

1 u = 1470 ÷ 7 = 210

Total number of $20-seat tickets
= 4 u
= 4 x 210
= 840

Number of $20-seat tickets sold
= 80% x 840
= ⁸⁰₁₀₀ x 840
= 672

Amount collected from $20-seat tickets sold
= 672 x 20
= $13440

Amount collected from $45-seat tickets sold
= 34905 - 13440
= $21465

Number of $45-seat tickets sold
= 21465 ÷ 45
= 477

Number of tickets sold
= 672 + 477
= 1149

Number of tickets left unsold
= 1470 - 1149
= 321

Answer(s): 321