Question

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.

Answer 1

Radius of the well = `2.8/2` = 1.4 m

Depth of the well = 28 m

Therefore, volume of earth dug out = πr²h

= `22/7 xx 1.4 xx 1.4 xx 28` 

= `17248/100`

= 172.48 m³

Area of curved surface = 2πrh

= `2 xx 22/7 xx 1.4 xx 28`

= 246.40 m²

Cost of plastering the rate of Rs. 4.50 per sq m 

= Rs. 246.40 × 4.50

= Rs. 1108.8