Question

Twenty-one cylindrical pillars of a building have to be cleaned. If the diameter of each pillar is $50cm$ and the height is $4m$, find the cost of cleaning them at the rate of $Rs.1.50per{m}^2$.

Answer 1

Diameter of pillar $=50cm$

Radius of pillar $=\frac{50}{2}=25cm=0.25m$

Height of pillar $=4m$

Curved surface area of one pillar

$=2\pi rh=2\times \frac{22}{7}\times 0.25\times 4=\frac{44}{7}{m}^2$

Curved surface area of $21$ pillars $=\frac{44}{7}\times 21=132m^2$

Cost of cleaning $=Rs.1.5$ per square meter

Therefore,

Cost of cleaning all pillars $=1.5\times 132=Rs.198$