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.
Inner radius of the well, r = `4.2/2`= 2.1 m
Depth of the well, h = 10 m
∴ Inner surface area of the well = 2πrh = 2 x `22/7` x 2.1 x 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.
Concept: Surface Area of a Cuboid
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