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प्रश्न
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.
उत्तर
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
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