Question

A bus stop is barricaded from remaining part of the road, by using $50$ hollow cones made of recycled cardboards. Each cone has a base diameter of $40cm$ and height $1m$. If the outer side of each of the cones is to be painted and the cost of painting is $12$ per $m^2$, what will be the cost of painting all these cones.

Answer 1

Given, diameter $=40cm$

Radius, $r=\frac{40}{2}cm=20cm=0.2m$
Height, $h=1m$

Slant height, $l=\sqrt{h^2+r^2}$

$=\sqrt{1^2+{0.2}^2}m=\sqrt{1.04}m$$=1.02m$

CSA $=\pi rl=(3.14\times 0.2\times 1.02)m^2$$=0.64056m^2$

CSA of $50$ cones $=50\times 0.64056m^2$

$=32.028m^2$

Cost of painting $1$m${}^2$ area $=Rs.12$

Cost of painting $32.028m^2$ area $=Rs.32.028\times 12$

$=Rs.384.336$$\approx Rs.384.34$