Which is the following is the best deal?
A: six small grapefruits for a $1
B: four medium grapefruits for a $1
C: Three large grapefruits for a $1
Assume that all the grapefruits are spherical, that the small grapefruits have a diameter of 3inches, the medium grapefruits have a diameter of 3.5 inches and the large grapefruits have a diameter of of 4 inches.