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Find the total surface area of a hemisphere and a solid hemisphere each of radius 10 cm. (Use π = 3.14)
Radius = 10 cm
Total surface area of a hemisphere = 2πr2
⇒ Total surface area of a hemisphere = 2 × 3.14 × 10 × 10 = 628 cm2
Total surface area of a solid hemisphere = 3πr2
⇒ Total surface area of a solid hemisphere = 3 × 3.14 × 10 × 10 = 942 cm2
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.