Question

A water well has a height of 8m and diameter of 3.5m. What is the cost of plastering its curved surface and base at the rate of ₹50/m^2? (Take π = \(\frac{22}{7}\))

(a) ₹15000

(b) ₹14500

(c) ₹14000

(d) ₹14700

I have been asked this question during an online interview.

My question comes from Surface Area of a Right Circular Cylinder topic in chapter Surface Areas and Volumes of Mathematics – Class 9

Answer 1

The correct option is (b) ₹14500

Explanation: The total area to be plastered = curved surface area + base area

= 2πrh + πr^2

= \((2 * \frac{22}{7} * 1.75 * 8) + {\frac{22}{7}*(8)^2}\)

= 88 + 201.14

= 289.14 m^2

≈ 290 m^2

The cost of plastering area of 1 m^2 = ₹50

Therefore, the cost of plastering area of 290 m^2 = 290 * 50

= ₹14500.