Question

The angular elevation is ${60}^{\circ }$. The internal and external radii of a hollow cylinder are $12cm$ and $18cm$ respectively. If its height is $14cm$, then find its curved surface area. (Take $\pi =\frac{22}{7})$

Answer 1

Let $r,R$ be the internal and external radius and $h$ be height.
$r=12$ cm, $R=18$ cm, $h=14$ cm
Curved Surface Area $=2\pi h(R+r)$ square unit
$=2\times \frac{22}{7}\times 14(18+12)$
$=2\times \frac{22}{7}\times 14\times 30$$
$=2640c{m}^2$