How many cubic metres of earth must be dug out to sink a well which is 20 m deep and has a diameter of 7 metres? If the earth so dug out is spread over a rectangular plot 28 m by 11 m, what is the height of the platform so formed?
It is given in the question that,
Diameter = 7m
Hence,
Radius = 3.5 m
Depth = 20 m
Volume of the earth to be dug out = 
= 
= 770 m3
Volume of the earth piled upon the given plot = 28× 11 × h
Therefore,
Height = 
= 
= 2.5 m
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