If the diameter of the base of cone is 10 cm and its height is 12 cm, then its curved surface area is

1. 60π cm²

2. 65π cm²

3. 90π cm²

4. 120π cm²

The radius of a hemispherical balloon increases from 6 cm to 12 cm as air is being pumped into it. The ratio of the surface areas of the balloon in the two cases is

1. 1 : 4

2. 1 : 3

3. 2 : 3

4. 2 : 1

If two solid hemispheres of same base radius r are joined together along with their bases, then the curved surface of this new solid is

1. 4πr²

2. 6πr²

3. 3πr²

4. 8πr²