Question

Along a path, 100 conical pillars are constructed. Each pillar has base radius 7 cm and height 24 cm.
find the total cost of painting these pillars @ of 120
per
cm2.
​

Answer 1

Answer:

Total cost of painting these pillars is ₹66,000

Step-by-step explanation:

Here, the each pillars are to be painted, so we'll calculate the lateral surface area of the conical pillars.

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Step 1 : Calculate the lateral surface area of a pillar :

• The pillars are cone-shaped.

Lateral surface area of cone : πr√r² + h²

Where,

• r (radius) = 7cm.
• h (height) = 24cm.
• Taking 'π' as 22/7.

So, the surface area of a cone is :

→ π × 7√7² + 24²

→ π × 7√49 + 576

→ π × 7√625

→ π × 7 × 25

→ 22/7 × 7 × 25

→ 22 × 25

→ 550cm²

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Step 2 : Calculate the surface area of 100 such conical pillars :

[Unitary method]

∵ If one conical pillar is of 550cm²

∴ 100 such pillars will be of : 550 × 100

= 55,000cm²

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Step 3 : Calculate the cost of painting the pillars :

[Unitary method]

∵ Cost of painting 1cm² is ₹120 (given)

∴ Cost of painting 550cm² will be:

= 550×120

= ₹66,000

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Answer 2

Question :

Along a path, 100 conical pillars are constructed. Each pillar has base radius 7 cm and height 24 cm. find the total cost of painting these pillars @ of 120percm2.

Formula used :

CSA of cone = πrl

l²= h²+r²

Where r = radius of cone

l = slant height of cone

Solution :

CSA of cone = πrl

= 22/7 × 7 × √ h²+r²

= 22/7×7 √ 24²+7²

= 22 × 25

= 550 cm ²

CSA of 100 pillars = 100× CSA of 1 cone

= 100 × 550

= 55000 cm ²

So , cost of painting the pillars

By applying unitary method

= CSA × cost of painting

= 550× 120

= 66000

So, cost of painting the pillars is 66000