The example of hollow cylinders is pipes, circular buildings and bearing bushes, etc. If is the outside radius of the cylinder and is the inside radius of the cylinder, then

(i)

(ii)

and being outer and inner diameter, is volume.

__Example__**:**

A well with **10m** inside diameter dug **14m** deep. Earth taken out of it is spread all round to a width of **5m** to form an embankment. Find the height of the embankment.

__Solution__**:**

Volume of the dug out

Area of the embankment (shaded)

Height of the embankment

__Example__**:**

A hollow cylinder copper pipe is **21dm** long. Its outer and inner diameters are **10cm** and **6cm** respectively. Find the volume of copper used in making the pipe.

__Solution__**:**

Given that:

Height of cylindrical pipe,

External radius,

Internal radius,

Volume of the copper used in making the pipe

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