Question

A lead pencil is in the shape of right circular cylinder. The pencil is $28cm$ long and its radius is $3mm$. If the lead is of radius $1mm$, then find the volume of the wood used in the pencil.

• A. $7.04{cm}^3$
• B. $7.14{cm}^3$
• C. $8.04{cm}^3$
• D. None of these

Answer 1

The correct option is A $7.04{cm}^3$

We have,

$h=28cm$

$R=3mm=0.3cm$

$r=1mm=0.1cm$

We know that the volume of the hollow cylinder

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

So,

$=\frac{22}{7}\times \left(\right(0.3{)}^2-\left(0.1{)}^2\right)\times 28$

$=22\times (0.09-0.01)\times 4$

$=88\times 0.08$

$=7.04c{m}^3$

Hence, this is the answer.