A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. Each cone has a base diameter of 40 cm and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is Rs 12 per m², what will be the cost of painting all these cones? ( use Pi as 22/7)

Diameter of base of each hollow cone = 40 cm = 0.40 m
then its radius;r = $\frac{0.40}{2}$ = 0.20 m
Height of cone;h = 1 m
So, slant height of cone is given by;
$$\begin{gathered} l = \sqrt{r^2+h^2} \\ \Rightarrow l = \sqrt{{\left(0.20\right)}^2+1^2} = \sqrt{1.04} = 1.019 \mathrm{m} \end{gathered}$$
surface area of each hollow cone = curved surface area of cone = $\mathrm{\pi rl} = \frac{22}{7}\times 0.20\times 1.019 = 0.6405 {\mathrm{m}}^2$
Therefore surface area of 50 hollow cones = $50\times 0.6405 = 32.025 {\mathrm{m}}^2$
Cost of painting per square metre = Rs.12
therefore total cost of painting 50 hollow cones = $32.025\times 12$ = Rs.384.30