# How Many Cubic Metres of Earth Must Be Dugout to Sink a Well 21 M Deep and 6 M Diameter? Find the Cost of Plastering the Inner Surface of the Well at Rs 9.50 per M2 - Mathematics

Sum

How many cubic metres of earth must be dugout to sink a well 21 m deep and 6 m diameter? Find the cost of plastering the inner surface of the well at Rs 9.50 per m2

#### Solution

Given data is as follows:

h = 21 m

Diameter = 6 m

Plastering rate = Rs.9.50/m2

We have to find the volume and the cost of plastering the inner surface of this well.

Given is the diameter, which is 6 m. Therefore,

r=6/2

r = 3

We know that,

Volume =pir^2h

=22/7 xx 3xx3xx21

Volume = 594 m3

We know that,

Curved Surface Area = 2pirh

= 2 xx 22/7 xx 3 xx 21

Curved Surface Area =396 m2

Total cost of plastering = ( Curved Surface Area ) × (Plastering rate )

=396 × 9.50

= 3762

Therefore, the volume of this well is 594 m3 and cost of plastering its inner surface is Rs.3762.

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#### APPEARS IN

RD Sharma Mathematics for Class 9
Chapter 19 Surface Areas and Volume of a Circular Cylinder
Exercise 19.2 | Q 17 | Page 21