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 m^{2}

#### Solution

Given data is as follows:

h = 21 m

Diameter = 6 m

Plastering rate = Rs.9.50/m^{2}

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 m^{3}

We know that,

Curved Surface Area = `2pirh`

= `2 xx 22/7 xx 3 xx 21`

Curved Surface Area =396 m^{2}

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

^{ =396 × 9.50}

^{ = 3762}

Therefore, the volume of this well is 594 m^{3}^{ }and cost of plastering its inner surface is Rs.3762.