The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports as shown in Fig 13.32. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of radius 5cm and height 7cm and is painted black.Find the cost of paint required if silver paint cost 25 paisa per `cm^2` and black paint cost 5 paisa per `cm^2`

Explanation

Area to be painted silver=8*Surface area of sphere.

=`8*4pir^2`

=`8*4*22/7*(21/2)^2`

=11088`cm^2`

Area to be painted black=8*Curved surface area of cylinder

=`8*2pirh`

=`8*2*22/7*15*7`

=`528cm^2`

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