In a circular sheet of paper of radius 20cm, a sector of 40% area is removed and the remaining part is used to make a conical surface. Find the volume of a conical surface.
Area of Circle (60% portion) = 60/100 × π × (20)² Now, Area of Circle (60% portion) = surface area of the cone (πrl) 
60/100 × π × (20)² = π ×r × 20 r = 12 cm Height of the cone = √(20²-12²) = √256 = 16cm Volume of the cone = 1/3 πr²h = 1/3 × π × 12 × 12 × 16 = 768 π
