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Sum

A cylindrical pillar has a radius of 21 cm and a height of 4 m. Find:

- The curved surface area of the pillar.
- cost of polishing 36 such cylindrical pillars at the rate of ₹12 per m
^{2}.

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#### Solution

r = 21 cm, h = 4 m = 400 cm

i. C.S.A = 2πrh

= `2 xx 22/7 xx 21 xx 400`

= 52800 cm^{2}

= `52800/(100 xx 100) = 5.28` m^{2}

ii. Rate = ₹12/m^{2}

Area to be polished = (5.28 × 36) m^{2}

Cost = 12 × Area

= 12 × 5.28 × 36

= ₹2280.96

Concept: Surface Area of a Cuboid

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