What is the surface area to volume ratio of a sphere?

Surface area to volume ratio of a sphere equals to ##3/r## where ##r## is the sphere’s radius.
Surface area of a sphere with radius ##r## equals to ##4pir^2##.
The volume of this sphere is ##4/3pir^3##.
Ratio of the surface area to volume therefore equals to
##(4pir^2)/(4/3pir^3)=4(3/4)(pi/pi)(r^2/r^3)=3/r##