Question

Find the cost of painting the outside surface of a solid cylinder of diameter $7$ m and height $25$ m at Rs.$8$ per square metre.

Answer 1

The formula of the outer surface area of the cylinder is $2\pi rh.$

To know that outer surface area we need to evaluate it.

Given that $d=7$

$\therefore r=\frac{d}{2}=\frac{7}{2}=3.5cm$

$h=25$ m

$\therefore$ outer surface area $=2\pi rh$

$=2\times \frac{22}{7}\times 3\times 5\times 25$

$=44\times 25\times 0.5$

$=550c{m}^2$

since the cost of painting is $8$ per $c{m}^2$

$=550\times 8$

= Rs. $4400$.