Q20 of 22 Page 258

A hollow cylindrical pipe has inner circumference 44 dm and outer 45 dm. Find the cost of painting it from both sides at Rs2 per m2. If its length is 3.5 m.

Given ; inner circumference = 2πr1 = 44

r1 = 7dm


outer circumference = 2πr2 = 45


r2 = 7.16dm


height (h) = 3.5m = 35 dm


Total area of painting pipe = inner curved surface area + outer curved surface area of cylinder


= 2π r1h + 2π r2h


= 2π h(r1 + r2)



= 22 × 14.16


= 311.52 dm2


As, cost of 1 dm2 = Rs 2


So, cost of 311.52 dm2 = Rs(2 × 311.52) = Rs. 623.04


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