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

Diameter of the circular pond is given = 40 m

So, the radius of this pond is 20 m

There is a path surrounding the pond. We are given the thickness of this path as 2 m

We have to grave this path with gravel. The depth of the path is also given 20 cm=0.2 m

This circular path can be viewed as a hollow cylinder of thickness 0.2 m and depth 0.2 m

We know,

Volume of a hollow cylinder $=\pi h\left(R^{2}-r^{2}\right)$

So the volume of the circular path with height 0.2 m

$=\pi \times 0.2\left(22^{2}-20^{2}\right)$

$=\pi \times 0.2\left(484-400^{2}\right)$

$=\pi \times 0.2 \times 84$

$=52.77 \mathrm{~m}^{3}$

Hence, the volume of gravel required is $52.77 \mathrm{~m}^{3}$