Question

The height of a cone is 30 cm. A small cone is cut off at the top by a plane parallel to the base. If its volume be 1/27 of the volume of the given cone, at what height above the base is the section made?

(A) 20 cm

(B) 25 cm

(C) 10 cm

(D) 15 cm

Answer 1

The correct option is: (A) 20 cm

Explanation: 

Let OC = h and AB = r

Now, ΔOAB ~ ΔOCD

Volume of smaller cone = 1/27 (Volume of whole cone)

Required height, AC = 30 - 10 = 20 cm