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Probability
Question
The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports as shown in figure. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of 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 costs 5 paise per cm2.
Solution
For a wooden sphere
Diameter = 21 cm
Radius (r) = 
∴ Surface area of a wooden sphere = 4
∴ Surface area of a wooden sphere to be painted = 1386 – 
(1.5)2
∴ Surface area of eight wooden spheres = 1378.93 x 8 = 11031.44 cm2 Cost of painting silver @ 25 paise per cm2 = 11031.44 x 25 paise
For a cylindrical support
Radius (r) = 1.5 cm Height (h) = 7 cm
Surface area of a cylindrical support = 2
rh
∴ Surface area of eight cylindrical supports = 66 x 8 = 528 cm2
∴ Cost of painting black @ 5 paise per cm2 = 528 x 5 paise
∴ Cost of paint required = 2757.86 + 26.40 = र 2784.26 (approx.)
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Mock Test Series
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