Question

A grand platform is supported by 70 cylindrical pillars of radius 20 cm and height 3.5 m. The cost of painting the CSA of the pillars at $₹6/m^2$ is

• A. ₹ 3640
• B. ₹ 3645
• C. ₹ 2640

Answer 1

The correct option is C ₹ 2640

Given
r = 0.2 m, h = 3.5 m, Number of pillars = 70
CSA of a cylinder $=2\pi rh$
$=2\times \pi \times 0.2\times 3.5$

CSA of 100 cylinders $=100\times 2\times \pi \times 0.2\times 3.5$
$=100\times 2\times \frac{22}{7}\times 0.2\times \frac{7}{2}$
$=100\times 2\times 11\times 0.2$
$=440m^2$
Cost for painting 1 m${}^2$ is ₹6.
$\therefore$ Total cost of painting 440 m${}^2$ $=440\times 6=₹2640$