Question

a well is 7.2 m deep . the cost of cementing its inner surface at 75 paisa per decimetre sq. is ₹ 11880.determine the radius of the well

Answer 1

Find the volume
Volume ×cost =total cost

Answer 2

Solution :-

Let r be the radius of the well.

Now,

Height = 7.2 m or 72 decimeter

Area cemented for Rs. 0.75 = 1 dm²

Area cemented for Rs. 11880 = 1*11880/0.75

= 11880/0.75

Curved Surface Area of the well = 15840 sq dm

Curved Surface Area of cylinder = 2πrh

15840 = 2*22/7*r*72

r = (15840*7)/3168

r = 110880/3168

r = 35 dm

So, Radius of the well is 35 decimeter or 3.5 m

Answer.