In this question we have to find cubic meters of gravel

which is required to grave the path to a depth of 20cm,

given that,

A path 2 m wide surrounds a circular pond of diameter 40 m.

One of the important question for the board exam class 10 from

mensuration chapter.This question is from r d sharma class 10 maths.

chapter-16 question number-28 maths r d sharma,mensuration.

Given,

Diameter of the circular pond = 40 m

So, the radius of the pond = 40/2 = 20 m = r

Thickness (width of the path) = 2 m

As the whole view of the pond looks like a hollow cylinder.

And the height will be 20 cm = 0.2 m

So,

Thickness (t) = R â€“ r

2 = R â€“ 20

R = 22 m

Volume of the hollow cylinder = Ï€ (R2â€“ r2) Ã— h

= Ï€ (222â€“ 202) Ã— 0.2

= 52.8 m3

Therefore, 52.8 cubic meters of gravel are required to grave the path to a depth of 20 cm.