The formula for the volume of a sphere is V=(4/3) (pi) r^3. if r is doubled then you get 2r as the radius and V=(4/3) (pi) * 8r^3 so the volume is eight times bigger than the original r value. if r is tripled the r =3r and (3r)^3 so the volume is 27 times bigger. If r is multiplied by n the radius is nr and (nr)^3 =n^3 r^3, Therefore, the volume is n^3 times bigger than the original.
