There are 20 cylindrical pillars in a building, each having a diameter of 50 cm and height 4 m.

Question:

There are 20 cylindrical pillars in a building, each having a diameter of 50 cm and height 4 m. Find the cost of cleaning them at ₹ 14 per m2.

Solution:

Radius of each pillar, $r=\frac{50}{2}=25 \mathrm{~cm}=0.25 \mathrm{~m} \quad(1 \mathrm{~m}=100 \mathrm{~cm})$

Height of each pillar, h = 4 m

$\therefore$ Surface area of each pillar $=2 \pi r h=2 \times \frac{22}{7} \times 0.25 \times 4 \mathrm{~cm}^{2}$

Surface area of 20 pillars = Surface area of each pillar $\times 20=2 \times \frac{22}{7} \times 0.25 \times 4 \times 20 \mathrm{~cm}^{2}$

Rate of cleaning = ₹ 14 per m2

∴ Total cost of cleaning the 20 pillars

= Surface area of 20 pillars × Rate of cleaning

$=2 \times \frac{22}{7} \times 0.25 \times 4 \times 20 \times 14$

$=₹ 1760$