Question

$10$ cylindrical pillars of 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. $5$ per square metre?

• A. Rs. $440$
• B. Rs. $480$
• C. Rs. $400$
• D. Rs. $500$

Answer 1

Answer: (A)

Given, diameter $=70$ cm

Thus $r=35$ cm $=\frac{35}{100}$ m $=\frac{7}{20}$ m
Also given $h=4$ m
Curved surface area of $1$ pillar $=2\pi rh$
Curved surface area of $10$ pillars $=10\times 2\pi rh=20\pi rh$
$\text{Cost}=$ Rs.$5\times 20\pi rh=$ Rs. $100\times \frac{22}{7}\times \frac{7}{20}\times 4$
$=$ Rs. $440$

Therefore, cost of painting at the rate of Rs. $5$ per square metre is Rs. $440$.