A dome of a building is in the form of a hemisphere. From inside, it was white-washed at the cost of र 498.96. If the cost of white-washing is र2.00 per square metre, find the
(i)    inside surface area of the dome,
(ii)    volume of the air inside the dome.

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’. 

A cube of side 4 cm contains a sphere touching its sides. Find the volume of the gap in between.