The volume of a sphere is given by V=4/3pie cubed. What happens to the volume of a sphere if r is halved?
You left out an r in your formula for volume.
If r is halved, the volume is reduced to a fraction (1/2)^3 = 1/8 of the original value.
If r is halved, the volume is reduced to a fraction (1/2)^3 = 1/8 of the original value.