1.25 gallons
so we know 0.5 gallons makes 1 pound, and we know that there are at least 2 pounds of butter made.
so we know that there is 1 full gallon of cream used.
however, there is also .5 pounds of butter, so we need to find out the other half.
to do this, we need to split the .5 gallons of cream in half, making 0.25
then, we add 1 + 0.25 gallons to equal 1.25 gallons of cream needed to make 2.5 pounds of butter