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25 cylindrical pillars of the building are to be cleaned. If the diameter of each pillar is 0.40 m and height is 5 m. Then, what is the cost of cleaning them at the rate of Rs. 3 per square meter?


1. Rs. 471
2. Rs. 475
3. Rs. 464
4. Rs. 481

1 Answer

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Correct Answer - Option 1 : Rs. 471

Given:

Diameter of each pillar = 0.4 m

∴ Radius of each pillar = r = 0.4/2 = 0.2 m

Height of the each pillar = 5 m

Formula used:

Area of cylinder = 2πrh

Calculation:

Curved surface area of each pillar = 2πrh

⇒ 2 × 3.14 × 0.2 × 5

⇒ 6.28 m2

Therefore, curved surface area of 25 pillar = 6.28 × 25 = 157 sq. m

Cost of cleaning = Rs. 3 per sq. m

∴ Cost of cleaning 25 pillars = Rs. 3 × 157

⇒ Rs. 471

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