Answer:
 33% off is the better deal
Step-by-step explanation:
1.33 times as much popcorn for the same price is equivalent to 1/1.33 ≈ 0.75 times the price for the original amount of popcorn. That price is equivalent to a sale of 1 - 0.75 = 0.25 = 25% off.
The sale price of 33% off is a better deal (if you don't want the extra popcorn).
