The internal and external diameters of a hollow hemispherical vessel are 21 cm and 28 cm respectively. Find :

(i) internal curved surface area,

(ii) external curved surface area,

(iii) total surface area,

(iv) volume of material of the vessel.

Metallic spheres of radii 6 cm, 8 cm and 10 cm respectively are melted and recasted into a single solid sphere. Taking π = 3.1, find the surface area of the solid sphere formed.

A cone and a sphere have equal volumes. Their radii are also equal each being 10 cm; the height of the cone is :

1. 70 cm

2. 40 cm

3. 50 cm

4. 20 cm