The museum tickets are priced at $13 and $7.  The number of $13-dollar tickets available is  1²₃ that of the number of $7-dollar tickets. 3 out of 4 of the $13-dollar tickets and all the $7-dollar tickets were sold. The ticket sales amounted to $2511. How much more would have been collected if all the tickets were sold?

	$13	$7
Comparing $13 and $7 tickets at first	5x4 = 20 u	3x4 = 12 u
Before	4x5 = 20 u
Change	- 3x5 = - 15 u	- 12 u
After	1x5 = 5 u	0 u

The number of 13 tickets at first is repeated.  Make the number of 13 tickets the same.  LCM of 4 and 5 is 20.

1²₃ = ⁵₃

Number of $13 tickets : $7 tickets = 5 : 3

	$13	$7	Total
Number	15 u	12 u
Value	$13	$7
Total value	195 u	84 u	$2511

Total amount collected from the sale of the sold tickets
= 195 u + 84 u
= 279 u

1 u = 2511 ÷ 279 = 9

Number of $13-tickets left unsold
= 5 u 
= 5 x 9
= 45

More amount to be collected if all the tickets were sold
= 45 x 13
= $585

Answer(s): $585