Q : 2 The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports as shown in Fig . Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of radius and height 7 cm and is to be painted black. Find the cost of paint required if silver paint costs 25 paise per and black paint costs 5 paise per .
Q : 3 The diameter of a sphere is decreased by . By what per cent does its curved surface area decrease?
Q : 1 A wooden bookshelf has external dimensions as follows: Height , Depth , Breadth (see Fig. ). The thickness of the plank is everywhere. The external faces are to be polished and the inner faces are to be painted. If the rate of polishing is paise per and the rate of painting is paise per , find the total expenses required for polishing and painting the surface of the bookshelf.