Question

Find the cost of painting $15$ cylindrical pillars of a building at $Rs.2.50$ per square metre if the diameter and height of each pillar are $48cm$ and $7$ metres respectively.

Answer 1

Given: Diameter of a cylindrical pillar $=48cm.$

$\therefore$ Radius $\left(r\right)=\frac{48}{2}=24cm=\frac{24}{100}m$

Height $\left(h\right)=7m$

$\therefore$ Lateral (Curved) surface area of one pillar [Painting is done on curved surface area]

$=2\pi rh=2\times \frac{22}{7}\times \frac{24}{100}\times 7m^2$

$=\frac{1056}{100}{m}^2$

Surface area of $15$ pillars

$=\frac{1056}{100}\times 15m^2=\frac{15840}{100}{m}^2$

Rate of painting $=Rs.2.50$ per $m^2$

$\therefore$ Total cost $=Rs.2.50\times \frac{15840}{100}$

$=Rs.396$