The drama centre had 1872 seats. There were 40% fewer $30-seats than $15-seats. 50% of the $15-seats and some $30-seats were sold. A total of $20835 was collected. How many seats were unsold?

	$30	$15	Total
Number	3 u	5 u	8 u

100% - 40% = 60%
⁶⁰₁₀₀ = ³₅

Total number of seats
= 3 u + 5 u
= 8 u

8 u = 1872

1 u = 1872 ÷ 8 = 234

Total number of $15-seat tickets
= 5 u
= 5 x 234
= 1170

Number of $15-seat tickets sold
= 50% x 1170
= ⁵⁰₁₀₀ x 1170
= 585

Amount collected from $15-seat tickets sold
= 585 x 15
= $8775

Amount collected from $30-seat tickets sold
= 20835 - 8775
= $12060

Number of $30-seat tickets sold
= 12060 ÷ 30
= 402

Number of tickets sold
= 585 + 402
= 987

Number of tickets left unsold
= 1872 - 987
= 885

Answer(s): 885