Question

In a building there are 30 cylindrical pillars. The radius of each pillar is 35 cm and height is 5 m. Find out the
cost of painting the curved surface of half the number of pillars. The rate of painting is Rs.10 per m² .

• A. Rs. 8250
• B. Rs. 16,500
• C. Rs. 1650
• D. Rs. 4125

Answer 1

The Correct Option is C

To find the cost of painting the curved surface of half the number of pillars, we first need to calculate the curved surface area of a single pillar and then determine the cost based on the given rate per square meter.

1. Identify the given values:
   • Number of cylindrical pillars: 30 
   • Radius of each pillar: 35 cm
   • Height of each pillar: 5 m
   • Rate of painting: Rs. 10 per m²
2. Convert the radius from centimeters to meters:
   • Radius = 35 cm = 0.35 m
3. Calculate the curved surface area (CSA) of one cylindrical pillar using the formula: \(CSA = 2\pi rh\), where \(r\) is the radius and \(h\) is the height.
   • \(CSA = 2 \times \frac{22}{7} \times 0.35 \times 5\)
   • \(CSA = 2 \times \frac{22}{7} \times 1.75\)
   • \(CSA = 2 \times 5.5\)
   • \(CSA = 11\, \text{m}^2\)
4. Calculate the total curved surface area for half the pillars (15 pillars):
   • Total CSA for 15 pillars = \(15 \times 11 = 165 \, \text{m}^2\)
5. Determine the cost of painting:
   • Total cost = \(165 \times 10 = \text{Rs. } 1650\)

Therefore, the cost of painting the curved surface of half the number of pillars is Rs. 1650.