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Question
The internal and external diameters of a hollow hemispherical vessel are 20 cm and 28 cm respectively. Find the cost to paint the vessel all over at ₹ 0.14 per cm2
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Solution
Internal radius (r) = `20/2` = 10 cm
External radius (R) = `28/2` = 14 cm
T.S.A of a hollow hemisphere
= π (3R2 + r2) sq.units
= `22/7[3 xx 14^2 + 10^2]` cm2
= `22/7[588 + 100]` cm2
= `22/7 xx 688` cm2
Cost of painting the vessel
= `₹ 0.14 xx 22/7 xx 688`
= `₹ 14/100 xx 22/7 xx 688`
= `₹ (2 xx 22 xx 688)/100`
= `₹ 30272/100`
= ₹ 302.72
Cost of painting = ₹ 302.72
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