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The surface area of a sphere is 5544 cm2, find its diameter.
Let the radius of the sphere be r cm.
We know that, surface area of a sphere = 4πr2
Given, surface area of a sphere is 5544 cm2
⇒ 4πr2 = 5544
⇒ 4× × r 2 = 5544
⇒ r2 = 441
⇒ r = 21 cm
Thus diameter = 42 cm
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.