Question

10 cylindrical pillars of the building have to be painted. The diameter of each pillar is 70 cm and the height is 4 m. What is the cost of painting at the rate of Rs 5 square meter?
a) Rs 400
b) Rs 440
c) Rs 480
d) Rs 500

Answer 1

Hint: We need to paint 10 cylindrical pillars whose diameter is 70 cm and height is 4 m. So, firstly find the curved surface area of all the 10 pillars by using the formula: $CSA=2\pi rh$ where r is the radius and h is the height of the cylinder. Now, we know that the cost of painting is Rs 5 per square meter. So, the total cost of painting is: $CSA\times \text{price}$.

Complete step-by-step solution
We have:

Diameter of cylindrical pillar: $d=70cm=0.7m$
So, radius of cylindrical pillar: $r=\dfrac{d}{2}=\dfrac{0.7}{2}=0.35m$
Height of cylindrical pillar: $h=4m$
So, by using the formula: $CSA=2\pi rh$
The curved surface area of a cylindrical pillar is:
$\begin{align}
  & CSA=2\pi \times 0.35\times 400 \\
 & =8.79{{m}^{2}}
\end{align}$
So, the curved surface area of 10 cylindrical pillars is:
$\begin{align}
  & CSA=8.79\times 10 \\
 & =87.9{{m}^{2}}
\end{align}$
Now, we need to find the total cost of painting the cylindrical pillars.
We know that the cost of painting is Rs 5 per square meter.
So, the cost of painting 10 pillars is:
$\begin{align}
  & Cost=CSA\times price \\
 & =87.9\times 5 \\
 & =Rs.43.95
\end{align}$
Hence, total cost of painting 10 pillars is Rs 879.2

Note: Remember to convert the radius of the cylindrical pillar from cm to m because the cost of painting is given as Rs 5 per square meter. It can be done another way vice versa. Convert the height into cm and cost of painting as Rs 5 per square meter to Rs 5 per 100 square centimeters. Then find the cost of painting per square centimeter and multiply with the curved surface area to get the total cost of painting.