The auditorium had 980 seats. There were 25% fewer $35-seats than $20-seats. 80% of the $20-seats and some $35-seats were sold. A total of $25445 was collected. How many seats were unsold?

	$35	$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 = 980

1 u = 980 ÷ 7 = 140

Total number of $20-seat tickets
= 4 u
= 4 x 140
= 560

Number of $20-seat tickets sold
= 80% x 560
= ⁸⁰₁₀₀ x 560
= 448

Amount collected from $20-seat tickets sold
= 448 x 20
= $8960

Amount collected from $35-seat tickets sold
= 25445 - 8960
= $16485

Number of $35-seat tickets sold
= 16485 ÷ 35
= 471

Number of tickets sold
= 448 + 471
= 919

Number of tickets left unsold
= 980 - 919
= 61

Answer(s): 61