Answer 1

Diameter of circular pond = 40 m 

Radius of pond(r) = 20m.

Thickness = 2m

Depth = 20cm = 0 2m

Since it is viewed as a hollow cylinder

Thickness (t) = R - r

2 = R - r

2 = R - 20

R = 22m

∴Volume of hollow cylinder = π(R² - r²)h

= π(22² - 20²)h

= π(22² - 20²) x 0.2

= π(84) x 0.2

∴ Volume of hollow cylinder = 52.πm³

∴ 52.77m³ of gravel is required to

have path to a depth of 20cm.