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CBSE Class 9 Answered

A hollow cylindrical tube, open at both ends is made of iron 1 cm thick. If the external diameter is 14 cm and the length of tube is 70 cm, Find the cost of painting its inner surface at the rate of Rs. 4 per cm2.

Asked by Topperlearning User | 12 Oct, 2017, 08:09: AM
Expert Answer

External diameter = 14 cm, Internal diameter = 12 cm.

Internal radius (r) = 6 cm, Length of the tube (h) = 70 cm

Let S be the inner curved surface area.

 

begin mathsize 12px style straight S space equals space 2 πrh
straight S space equals space 2 cross times 22 over 7 cross times 6 cross times 70 space cm squared
straight S space equals space 2640 space cm squared end style

 

Cost of painting 1 cm2 = Rs. 4

Therefore, cost of painting 2640 cm2 = Rs. (2640 x 4) = Rs. 10560

Answered by | 12 Oct, 2017, 10:09: AM
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