Twenty one cylindrical pillars of the Parliament House are to be cleaned. If the diameter of each pillar is 0.50 m and height is 4 m, what will be the cost of cleaning them at the rate of Rs 2.50 per square metre?
Solution
\[\text{ Given } : \]
\[\text{ Diameter of the pillars = 0 . 5 m} \]
\[\text{ Radius of the pillars, r = 0 . 25 m } \]
\[\text{ Height of the pillars, h = 4 m } \]
\[\text{ Number of pillars } = 21\]
\[\text{ Rate of cleaning = Rs 2 . 50 per square metre } \]
\[\text{ Curved surface area of one pillar } = 2\pi rh\]
\[ = 2 \times \frac{22}{7} \times 0 . 25 \times 4\]
\[ = 2 \times \frac{22}{7}\]
\[ = \frac{44}{7} m^2 \]
\[ \therefore \text{ Curved surface area of one pillar } = \frac{44}{7} \text{ m} ^2 \]
\[\text{ Cost of cleaning 21 pillars at the rate of Rs 2 . 50 per m}^2 = \text{ Rs } 2 . 5 \times 21 \times \frac{44}{7} \]
\[ = 7 . 5 \times 44\]
\[ \therefore \text{ Cost of cleaning 21 pillars at the rate of Rs 2 . 50 per m} ^2 = Rs 330\]
