Question

Find the cost of plastering the inner surface of a well at Rs 9.50 per m², if it is 21 m deep and diameter of its top is 6 m.

Answer 1

\[\text{ Given } : \]
\[ \text{ Height, h = 21 m} \]
\[\text{ Diameter, d = 6 m} \]
\[ \text{ Radius, r = 3 m } \]
\[\text{ Area of the inner surface of the well, } S = 2\pi rh\]
\[ = 2\pi \times 3 \times 21 m^2 \]
\[ = 2 \times \frac{22}{7} \times 3 \times 21 m^2 \]
\[ = 396 m^2 \]
\[\text{ According to question, the cost per } m^2 \text{ is Rs }  9 . 50 . \]
\[ \therefore \text{ Inner surface cost is Rs 396  } \times 9 . 50 = \text{ Rs }  3762\]