The museum tickets are priced at $15 and $13.  The number of $15-dollar tickets available is  2¹₂ that of the number of $13-dollar tickets. 3 out of 7 of the $15-dollar tickets and all the $13-dollar tickets were sold. The ticket sales amounted to $1221. How much more would have been collected if all the tickets were sold?

	$15	$13
Comparing $15 and $13 tickets at first	5x7 = 35 u	2x7 = 14 u
Before	7x5 = 35 u
Change	- 3x5 = - 15 u	- 14 u
After	4x5 = 20 u	0 u

The number of 15 tickets at first is repeated.  Make the number of 15 tickets the same.  LCM of 7 and 5 is 35.

2¹₂ = ⁵₂

Number of $15 tickets : $13 tickets = 5 : 2

	$15	$13	Total
Number	15 u	14 u
Value	$15	$13
Total value	225 u	182 u	$1221

Total amount collected from the sale of the sold tickets
= 225 u + 182 u
= 407 u

1 u = 1221 ÷ 407 = 3

Number of $15-tickets left unsold
= 20 u 
= 20 x 3
= 60

More amount to be collected if all the tickets were sold
= 60 x 15
= $900

Answer(s): $900