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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 4.4cm. (see fig. 13.11). Find its (i) inner curved surface area, (ii) outer curved surface area (iii) total surface area (Assume π=22/7) Q.3

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Hello sir i want to know the best solution of the question from exercise 13.2   of math of Surface areas and Volumes chapter of class 9th give me the best and easy for solving this question how i solve it of question no.3  A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4cm. (see fig. 13.11). Find its (i) inner curved surface area, (ii) outer curved surface area (iii) total surface area (Assume π=22/7)

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1. Let r1 and r2 Inner and outer radii of cylindrical pipe

r1 = 4/2 cm = 2 cm

r2 = 4.4/2 cm = 2.2 cm

Height of cylindrical pipe, h = length of cylindrical pipe = 77 cm

(i) curved surface area of outer surface of pipe = 2πr1h

= 2×(22/7)×2×77 cm2

= 968 cm2

(ii) curved surface area of outer surface of pipe = 2πr2h

= 2×(22/7)×2.2×77 cm2

= (22×22×2.2) cm2

= 1064.8 cm2

(iii) Total surface area of pipe = inner curved surface area+ outer curved surface area+ Area of both circular ends of pipe.

= 2r1h+2r2h+2π(r12-r22)

= 9668+1064.8+2×(22/7)×(2.22-22)

= 2031.8+5.28

= 2038.08 cm2

Therefore, the total surface area of the cylindrical pipe is 2038.08 cm2.

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