The zoo tickets are priced at $21 and $17.  The number of $21-dollar tickets available is  2¹₂ that of the number of $17-dollar tickets. 3 out of 4 of the $21-dollar tickets and all the $17-dollar tickets were sold. The ticket sales amounted to $902. How much more would have been collected if all the tickets were sold?

	$21	$17
Comparing $21 and $17 tickets at first	5x4 = 20 u	2x4 = 8 u
Before	4x5 = 20 u
Change	- 3x5 = - 15 u	- 8 u
After	1x5 = 5 u	0 u

The number of 21 tickets at first is repeated.  Make the number of 21 tickets the same.  LCM of 4 and 5 is 20.

2¹₂ = ⁵₂

Number of $21 tickets : $17 tickets = 5 : 2

	$21	$17	Total
Number	15 u	8 u
Value	$21	$17
Total value	315 u	136 u	$902

Total amount collected from the sale of the sold tickets
= 315 u + 136 u
= 451 u

1 u = 902 ÷ 451 = 2

Number of $21-tickets left unsold
= 5 u 
= 5 x 2
= 10

More amount to be collected if all the tickets were sold
= 10 x 21
= $210

Answer(s): $210