# The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find (i) Its inner curved surface area, (ii) The cost of plastering this curved surface at the rate of Rs 40 per m^2. - Mathematics

The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find

(i) Its inner curved surface area,

(ii) The cost of plastering this curved surface at the rate of Rs 40 per m2.

["Assume "pi=22/7]

#### Solution

Inner radius (r) of circular well = (3.5/2)m = 1.75m

Depth (h) of circular well = 10 m

Inner curved surface area = 2πrh

=(2xx22/7xx1.75xx10)m^2

= (44 × 0.25 × 10) m2

= 110 m2

Therefore, the inner curved surface area of the circular well is 110 m2.

Cost of plastering 1 m2 area = Rs 40

Cost of plastering 110 m2 area = Rs (110 × 40)

= Rs 4400

Therefore, the cost of plastering the CSA of this well is Rs 4400.

Concept: Surface Area of Cylinder
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#### APPEARS IN

NCERT Class 9 Maths
Chapter 13 Surface Area and Volumes
Exercise 13.2 | Q 7 | Page 217