The total surface area of a cone whose radius is $\dfrac{r}{2}$ and slant height 2l is

1. 2πr(l + r)

2. $πr \Big(l + \dfrac{r}{4}\Big)$

3. πr(l + r)

4. 2πrl

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

If the ratio of the diameters of the two spheres is 3 : 5, then the ratio of their surface areas is

1. 3 : 5

2. 5 : 3

3. 27 : 125

4. 9 : 25

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