Question

15. The height of a hollow cylinder is 20 cm. If its outer radius is 7 cm and
its thickness is 2 cm, then find the whole surface and volume of cylinder.​

Answer 1

Given:

The height of a hollow cylinder is 20 cm.

If its outer radius is 7 cm and its thickness is 2 cm

To find:

The whole surface and volume of the cylinder

Solution:

The height of the hollow cylinder, h = 20 cm

The outer radius, R = 7 cm

The thickness = 2 cm

∴ The inner radius, r = 7 - 2 = 5 cm

Find the whole surface area of the hollow cylinder:

The whole surface area of the hollow cylinder is,

= T.S.A. of a cylinder

= $2 \pi (R + r)(h + R - r)$

= $2 \times \frac{22}{7} (7 + 5)(20 + 7 - 5)$

= $2 \times \frac{22}{7} \times 12\times 22$

= $\boxed{\bold{1659.42\: cm^2}}$

Finding the volume of the hollow cylinder:

The volume of the hollow cylinder is,

= $\pi (R^2 - r^2) h$

= $\frac{22}{7} \times (7^2 - 5^2) \times 20$

= $\frac{22}{7} \times 24 \times 20$

= $\boxed{\bold{1508.57\: cm^3}}$

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