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Question
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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