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A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm (see Fig.). Find its (i) inner curved surface area, (ii) outer curved surface area, (iii) total surface area.

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Length of metal pipe, l = 77 cm, 

h = 77 cm. 

Inner diameter = 4 cm, 

∴ r1 = 2 cm. 

Outer diameter= 4.4 cm. 

∴ r2 = 2.2 cm. 

(i) Inner surfce area of pipe (C.S.A) = 2πr1h

= 2 × 22 × 2 × 11 = 968 cm2

(ii) Outer surface area of pipe (C.S.A) = 2πr2h

= 2 × 22 × 2.2 × 11 = 44 × 24.2 = 1064.8 cm2

(iii) Total Surface area of Pipe (T.S.A.) 

= Inner CSA + Outer CSA + Area of circular ring. 

= 2πr1h + 2πr2h + (2πr2 2h – 2πr1 2h)

= 2032.8 + 5.28 

∴ T.S.A. = 2038.08 cm2 .

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