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A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of the plating it on the inside at the rate of Rs. 4 per 100 cm2.
Surface area of a hemisphere = 2πr2
Given, diameter of the hemisphere bowl is 10.5 cm
Surface area of the bowl = 2 × (22/7) × (10.5/2)2 = 173.25 cm2
Given, cost of the plating it on the inside at the rate of Rs. 4 per 100 cm2
Cost of plating the hemisphere bowl
The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports as shown in Fig. 21.11. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of a radius 1.5 cm and height 7 cm and is to be painted black. Find the cost of paint required if silver paint costs 25 paise per cm2 and black paint cost 5 paise per cm2.