**Twenty seven solid iron spheres, each of radius r and surface area S are melted to form a sphere with surface area S′. Find the**

**(i) radius r ′ of the new sphere, (ii) ratio of S and S′.**

**Solution (i)**

Twenty seven solid iron spheres, each of radius r, are melted to form a bigger sphere of radius r'. It means that combined volume of 27 spheres is equal to volume of new sphere.

Therefore, 27 (volume of 1 sphere of radius r) = Volume of new sphere of radius r'

**Solution (ii)**

Surface area of smaller sphere

Surface area of new sphere