If the ratio of volumes of two spheres is 1 : 8, then the ratio of their surface areas is :

1. 1 : 2

2. 1 : 4

3. 1 : 8

4. 1 : 16

Three solid spherical beads of radii 3 cm, 4 cm and 5 cm are melted and recast into a single spherical bead. Its radius is :

1. 6 cm

2. 7 cm

3. 8 cm

4. 9 cm

If a solid sphere of radius 10 cm is moulded into 8 spherical solid balls of equal radius, then the surface area of each ball (in cm²) is :

1. 50 π

2. 60 π

3. 75 π

4. 100 π