How many cubic meters of earth must be dug out to make a well 28 m deep and 2.8 m in diameter ? Also, find the cost of plastering its inner surface at Rs 4.50 per sq meter.
Radius of the well = `2.8/2=1.4 m`
`"Depth of the well=28 m"`
`"Therefore, volume of earth dug out "=pir^2h`
`"Area of curved surface"=2pirh`
Cost of plastering at the rate of `Rs.450` per sq m