Final answer:
To calculate the amount saved, multiply the original price of the season pass by the discount percentage. In this case, you would save $18 on a $90 season pass with a 20% discount.
Step-by-step explanation:
To calculate the amount saved, we need to find 20% of $90. 
 20% of $90 can be found by multiplying $90 by 20% (or 0.2). 
 So, 20% of $90 is $18. 
Therefore, you would save $18 when purchasing a season pass on discount.