# 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 ₹ 40 per m².

**Solution:**

Since the well is cylindrical its curved surface area with base radius 'r' and height 'h' is 2πrh.

Diameter of the well, d = 3.5 m

Radius of the well, r = d/2 = 3.5/2 m = 1.75 m

Depth of the well, h = 10 m

i) The inner curved surface area of the well = 2πrh

= 2 × 22/7 × 1.75 m × 10 m

= 110 m²

ii) We can calculate the cost of plastering by multiplying the curved surface area of the well and the rate of plastering per square meter.

Cost of plastering the curved surface area at ₹ 40 per m^{2} = 110 × 40 = ₹ 4400

Thus, the inner curved surface area is 110 m^{²} and the cost of plastering the circular well is ₹ 4400.

**Video Solution:**

## 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 ₹ 40 per m².

### Class 9 Maths NCERT Solutions - Chapter 13 Exercise 13.2 Question 7:

**Summary:**

It is given that inner diameter of a circular well is 3.5 m and it is10 m deep. We have found that the inner curved surface area is 110 m^{²} and the cost of plastering the circular well is ₹ 4400.