Question

The inner diameter of a well is 4.20 metre and its depth is 10 metre. Find the inner surface area of the well. Find the cost of plastering it from inside at the rate Rs.52 per sq.m.

Answer 1

Inner radius of the well, r = $\frac{4.2}{2}$ = 2.1 m

Depth of the well, h = 10 m

∴ Inner surface area of the well = 2$\mathrm{\pi }$rh = $2\times \frac{22}{7}\times 2.1\times 10$ = 132 m²

Rate of plastering = Rs 52/m²

∴ Cost of plastering the well from inside

= Inner surface area of the well × Rate of plastering

= 132 × 52

= Rs 6,864

Thus, the inner surface area of the well is 132 m² and the cost of plastering the well from inside is Rs 6,864.