The radius of a sphere is 2r, then its volume is equal to :

1. $\dfrac{4}{3}$ πr³

2. 4πr³

3. $\dfrac{8πr^3}{3}$

4. $\dfrac{32πr^3}{3}$

If the total surface area of a cube is 96 cm², then the volume of cube is

1. 8 cm³

2. 512 cm³

3. 64 cm³

4. 27 cm³

The diameters of two solid spheres are in the ratio 5 : 7. The ratio between areas of their curved surfaces is :

1. 5 : 7

2. 7 : 5

3. 49 : 25

4. 25 : 49

The radius of a cylinder is doubled and its curved surface area is kept as same, the height of the cylinder is:

1. same

2. doubled

3. halved

4. none of these