Question

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 and total surface area. (Take $\pi =\frac{22}{7}$)

Answer 1

Let $r,R$ and $h$ be the internal, external radii and the height of a hollow cylinder respectively.

Given that $r=12cm$, $R=18cm$, $h=14cm$

Now, curved surface area, $CSA=2\pi h(R+r)$

Thus, $CSA=2\times \frac{22}{7}\times 14\times (18+12)$

$=2640sq.cm$

Total surface area, $TSA=2\pi (R+r)(R-e+h)$

$=2\times \frac{22}{7}\times (18+12)(18-12+14)$

$=2\times \frac{22}{7}\times 30\times 20=\frac{26400}{7}$

Thus, the total surface area $=3771\frac{3}{7}sq.cm$