Question

The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find the cost of plastering its inner curved surface at Rs 4 per square metre.

 

Answer 1

\[\text{ Given: } \]
\[\text{ Inner diameter of the circular well }= 3 . 5 m\]
\[ \therefore \text{ Inner radius of the circular well, } r = 1 . 75 m\]
\[\text{ Depth of the circular well, } h = 10 m\]
\[\text{ Inner curved surface area } , S = 2\pi rh\]
\[S = 2\pi \times 1 . 75 \times 10 m^2 = 2 \times \frac{22}{7} \times 1 . 75 \times 10 m^2 \]
\[ = 110 m^2 \]
\[\text{ Cost of plastering  1 m}^2 \text{ area = Rs } 4\]
\[\text{ Cost of plastering  110 m}^2 \text{ area = Rs } \left( 110 \times 4 \right) = \text{ Rs } 440\]