A beach cooler is 2.5 ft long, 1.5ft wide and 2 ft tall. How much ice is needed to fill the cooler at least 1/3 fill? What are the assumptions you make.
Assume the ice packs closely enough that it fills the space involved.
Since the volume of the chest is 2.5*1.5*2 = 7.5 ft^3, we will need at least 1/3 of that, or 2.5 ft^3 of ice.