Discussion
A cylindrical pillar is 1m in diameter and 4.2m in height. The cost of white washing the curved surface of the pillar at the rate of ₹15 per m2, is
Answer: A
The cost is ₹ 198.
The curved surface area of a cylinder is \(2\pi r h\), which is \(\pi d h\) in terms of the diameter:
\[ \begin{aligned} \text{area} &= \frac{22}{7} \times 1 \times 4.2 = 13.2\ \text{m}^2 \\ \text{cost} &= 13.2 \times 15 = 198 \end{aligned} \]
The options 19.8 and 1.98 are the same digits with the decimal point misplaced, and 200 is a rounded figure. Only the curved surface is whitewashed, so the top and bottom circles are not added.
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