Q6 of 67 Page 195

The diameter of a solid metallic hemisphere is 42 cm. Find the cost of polishing its total surface at 20 paise per square cm.

Diameter of hemisphere = 42 cm


Radius of hemisphere = r = = 21 cm


Total surface area of hemisphere = 3πr2


= 3 × × 212


= 3 × 22 × 3 × 21


= 4158 cm2


Cost of polishing 1 sq. cm is 20 paise


⇒ cost of polishing 4158 cm2 = 4158 × 20


= 83160 paise


100 paise is 1 Rs


⇒ 83160 paise = = 831.6 Rs


Therefore, cost of polishing its total surface is 831.6 Rs


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