If the radius of a sphere is doubled, what is the ratio of the volume of the first sphere to that of the second sphere?

Explanation

Let the original radius be r
so the original volume ='4/3(πr^3)'
New radius= '2r'
so, new volume='4/3(π(2r)^3)'
Ratio
='{4/3(πr^3)}/{4/3(π8r^3)}'
='1/8'
so ratio = '1:8'