Question

10 cylindrical pillars of a building have to be painted. The diameter of each pillar is 70 cm and the height is 4m. What is the cost of painting at the rate of Rs. 10 per square metre?

Answer 1

Answer:

Answer –880

Explanation :

CSA of 10 cyc= 10*2πrh

= 2 * 22/7 * 35/100 * 4

= 44*35*4/(700)

= 10*176*35/700

= 176*35 /70

Cost = 10*176*35/70

= 880rs 

Answer 2

ANSWER:

Given:

• 10 cylindrical pillars
• Diameter of each pillar = 70cm = 0.7m
• Height of each pillar = 4m
• Cost of painting per sq. metre = Rs 10

To Find:

• Cost of painting all 10 pillars

Diagram:

$\setlength{\unitlength}{1mm}\begin{picture}(5,5)\thicklines\multiput(-0.5,-1)(26,0){2}{\line(0,1){40}}\multiput(12.5,-1)(0,3.2){13}{\line(0,1){1.6}}\multiput(12.5,-1)(0,40){2}{\multiput(0,0)(2,0){7}{\line(1,0){1}}}\multiput(0,0)(0,40){2}{\qbezier(1,0)(12,3)(24,0)\qbezier(1,0)(-2,-1)(1,-2)\qbezier(24,0)(27,-1)(24,-2)\qbezier(1,-2)(12,-5)(24,-2)}\multiput(16,2)(0,32){2}{\sf{0.35m}}\put(7,17.5){\sf{4m}}\end{picture}$

Concept(Approach used):

We are given that, the cylindrical pillars are to be painted. So, we will first find the Curved(or Lateral) Surface Area of 1 pillar. Then we will multiply it with the cost of painting. After that we will multiply the cost of painting 1 pillar with 10 so that we get the total cost, which will be our answer.

So, lets begin!!

Solution:

We are given that the diameter of the pillars is 70cm(0.7m).

So,

⇒ radius(r) = diameter/2 = 0.7m/2 = 0.35m.

And,

⇒ height(h) = 4m

Hence,

⇒ Curved Surface Area of a cylinder = 2πrh

Here, r = 0.35m, h = 4m, π = 22/7

Therefore,

⇒ CSA of 1 cylindrical pillar = 2 * 22/7 * 0.35 * 4

⇒ CSA of 1 cylindrical pillar = 2 * 22/7 * 35/100 * 4

⇒ CSA of 1 cylindrical pillar = 2 * 22 * 5/100 * 4

⇒ CSA = 22 * 1/10 * 4

⇒ CSA of 1 cylindrical pillar = 8.8m²

Now,

⇒ Cost of painting 1m² = Rs 10

⇒ Cost of painting 8.8m² = Rs 10 * 8.8

⇒ Cost of painting 8.8m² = Rs 88

Hence,

⇒ Cost of painting 1 cylindrical pillar = Rs 88

Now,

⇒ Cost of painting 10 cylindrical pillars = Rs 88 * 10

⇒ Cost of painting 10 cylindrical pillars = Rs 880

Hence, cost of painting 10 cylindrical pillars is Rs 880.

Formula Used:

• Curved Surface Area of a cylinder = 2πrh

Learn More:

• Curved Surface Area of a cylinder = 2πrh
• Total Surface Area of a cylinder = 2πrh + πr²
• Volume of a cylinder = πr²h