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

Given: Inner diameter (d) = 4.2 m, 

To find: depth (h) = 10 m, rate of plastering = Rs 52 per sq.m. 

Inner surface area and total cost of plastering 

i. Inner curved surface area of the well = 2πrh 

= πdh … [∵ d = 2r]

= \(\sqrt[22]{7}\) x 4.2 x 10

= \(\sqrt[22]{7}\) x 42

= 22 x 6 

= 132 sq.m. 

ii. Rate of plastering = Rs 52 per sq.m. 

∴ Total cost = Curved surface area x Rate of plastering 

= 132 x 52 = Rs 6864 

∴ The cost of plastering the well from inside is Rs 6864.