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 48 cm and 7 metres respectively.
Solution:
Diameter $=48 \mathrm{~cm}$
Radius $=24 \mathrm{~cm}=0.24 \mathrm{~m}$
Height $=7 \mathrm{~m}$
Now, we have:
Lateral surface area of one pillar $=\pi \mathrm{dh}=\frac{22}{7} \times 0.48 \times 7=10.56 \mathrm{~m}^{2}$
Surface area to be painted $=$ total surface area of 15 pillars $=10.56 \times 15=158.4 \mathrm{~m}^{2}$
$\therefore$ Total cost $=$ Rs $(158.4 \times 2.5)=$ Rs 396