$10$ cylindrical pillars of building have to be painted. The diameter of each pillar is $70$ cm and the height is $4$ m. What is the cost of painting at the rate of Rs. $5$ per square metre?

Rs.

400

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Rs.

440

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Rs.

480

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Rs.

500

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Solution

The correct option is A Rs. $440$
Given, diameter $= 70$ cm
Thus $r = 35$ cm $= \frac{35}{100}$ m $= \frac{7}{20}$ m
Also given $h = 4$ m
Curved surface area of $1$ pillar $= 2 π r h$
Curved surface area of $10$ pillars $= 10 \times 2 π r h = 20 π r h$
$Cost =$ Rs. $5 \times 20 π r h =$ Rs. $100 \times \frac{22}{7} \times \frac{7}{20} \times 4$
$=$ Rs. $440$
Therefore, cost of painting at the rate of Rs. $5$ per square metre is Rs. $440$ .

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