The concert hall tickets are priced at $20 and $13.  The number of $20-dollar tickets available is  1³₅ that of the number of $13-dollar tickets. 3 out of 4 of the $20-dollar tickets and all the $13-dollar tickets were sold. The ticket sales amounted to $555. How much more would have been collected if all the tickets were sold?

	$20	$13
Comparing $20 and $13 tickets at first	8x1 = 8 u	5x1 = 5 u
Before	4x2 = 8 u
Change	- 3x2 = - 6 u	- 5 u
After	1x2 = 2 u	0 u

The number of 20 tickets at first is repeated.  Make the number of 20 tickets the same.  LCM of 4 and 8 is 8.

1³₅ = ⁸₅

Number of $20 tickets : $13 tickets = 8 : 5

	$20	$13	Total
Number	6 u	5 u
Value	$20	$13
Total value	120 u	65 u	$555

Total amount collected from the sale of the sold tickets
= 120 u + 65 u
= 185 u

1 u = 555 ÷ 185 = 3

Number of $20-tickets left unsold
= 2 u 
= 2 x 3
= 6

More amount to be collected if all the tickets were sold
= 6 x 20
= $120

Answer(s): $120