The zoo tickets are priced at $10 and $7.  The number of $10-dollar tickets available is  1¹₃ that of the number of $7-dollar tickets. 2 out of 5 of the $10-dollar tickets and all the $7-dollar tickets were sold. The ticket sales amounted to $1665. How much more would have been collected if all the tickets were sold?

	$10	$7
Comparing $10 and $7 tickets at first	4x5 = 20 u	3x5 = 15 u
Before	5x4 = 20 u
Change	- 2x4 = - 8 u	- 15 u
After	3x4 = 12 u	0 u

The number of 10 tickets at first is repeated.  Make the number of 10 tickets the same.  LCM of 5 and 4 is 20.

1¹₃ = ⁴₃

Number of $10 tickets : $7 tickets = 4 : 3

	$10	$7	Total
Number	8 u	15 u
Value	$10	$7
Total value	80 u	105 u	$1665

Total amount collected from the sale of the sold tickets
= 80 u + 105 u
= 185 u

1 u = 1665 ÷ 185 = 9

Number of $10-tickets left unsold
= 12 u 
= 12 x 9
= 108

More amount to be collected if all the tickets were sold
= 108 x 10
= $1080

Answer(s): $1080