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20. An iron pipe 20cm long has exterior dian eter equal to 25cm. If the thickness of the pipe is lcm,find the whole surface of the pipe. |
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Answer» Solution:- Height of pipe = 20 cmExternal diameter = 25 cmExternal radius = 25/2 = 12.5 cmInternal diameter = 25 - (1 + 1)= 23 cmInternal radius = 23/2 = 11.5 cm Let the external radius be R and the internal radius be r.Total surface area of the pipe = 2πh(R + r) + 2π(R² - r²)⇒ 2*22/7*20(12.5 + 11.5) + 2*22/7*{(12.5)² - (11.5²)⇒ (44*480)/7 + (44*24)/7⇒ 21120/7 + 1056/7⇒ 22176/7= 3168 cm²So, the total surface area of the pipe is 3168 square cm. |
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