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The dome of a building is in the form of a hemisphere. Its radius is 63 dm. Find the cost of painting it at the rate of Rs. 2 per sq. m.
Surface area of a hemisphere = 2πr2
Given, dome of a building is in the form of a hemisphere. Its radius is 63 dm.
1 dm = 0.1m
Thus, 63 dm = 6.3 m
Surface area of the dome = 2 × (22/7) × (6.3)2 = 249.48 m2
Cost of painiting it at Rs. 2 per sq. m. = 249.48 × 2 = Rs. 498.96
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.