320 portions of waffles can be made with one container.
Step-by-step explanation:
Given,
Milk is bought in 1 gallon container.
One portion of waffles require = 0.4 ounces of milk
We know that;
1 gallon = 128 ounces
Now;
No. of portions of waffles = 
No. of portions of waffles = 
No. of portions of waffles = 320
320 portions of waffles can be made with one container.