A solid right circular cone is cut into two parts at the middle of its height by a plane parallel to its base. The ratio of the volume of the smaller cone to the whole cone is:  1:2        (b)  1:4    (c)  1:6      (d)  1:8

Explanation

For larger cone,`tan(theta)= R/h`
For smaller cone,`tan(theta)=r/(h/2)=2r/h`
Hence, `R=2r`

Required ratio= `(1/3*r^2*h/2)/(1/3*R^2*h)`
Therefore, Requied Ratio=1/8.