Final answer:
The students ate 5 1/2 gallons of ice cream before lunch.
Step-by-step explanation:
To find out how many gallons of ice cream the students ate before lunch, we first need to calculate the amount they ate. If they ate 1/3 of 16 1/2 gallons of ice cream, we can find this by multiplying 1/3 by the total amount of ice cream.
1/3 x 16 1/2 = 16 1/2 ÷ 3 = 5 1/2 gallons
Therefore, the students ate 5 1/2 gallons of ice cream before lunch.