The concert hall tickets are priced at $21 and $14.  The number of $21-dollar tickets available is  2²₃ that of the number of $14-dollar tickets. 3 out of 5 of the $21-dollar tickets and all the $14-dollar tickets were sold. The ticket sales amounted to $1428. How much more would have been collected if all the tickets were sold?

	$21	$14
Comparing $21 and $14 tickets at first	8x5 = 40 u	3x5 = 15 u
Before	5x8 = 40 u
Change	- 3x8 = - 24 u	- 15 u
After	2x8 = 16 u	0 u

The number of 21 tickets at first is repeated.  Make the number of 21 tickets the same.  LCM of 5 and 8 is 40.

2²₃ = ⁸₃

Number of $21 tickets : $14 tickets = 8 : 3

	$21	$14	Total
Number	24 u	15 u
Value	$21	$14
Total value	504 u	210 u	$1428

Total amount collected from the sale of the sold tickets
= 504 u + 210 u
= 714 u

1 u = 1428 ÷ 714 = 2

Number of $21-tickets left unsold
= 16 u 
= 16 x 2
= 32

More amount to be collected if all the tickets were sold
= 32 x 21
= $672

Answer(s): $672