 # RS Aggarwal Solutions Class 9 Mathematics Solutions for Volume And Surface Area Of Solids Exercise 15B in Chapter 15 - Volume And Surface Area Of Solids

Question 6 Volume And Surface Area Of Solids Exercise 15B

There are 20 cylindrical pillars in a building, each having a diameter of 50cm and height 4m. Find the cost of cleaning them at ₹ 14 per m2.

It is given that

Diameter of one pillar = 50cm = 0.5m

So the radius of one pillar = 0.5/2 = 0.25m

Height of one pillar = 4m

We know that

Lateral surface area of one pillar = 2 πrh

By substituting the values

Lateral surface area of one pillar = 2 × (22/7) × 0.25 × 4

So we get

Lateral surface area of one pillar = 6.285 m2

So the lateral surface area of 20 pillars = 20 × 6.285 = 125.714 m2

It is given that the cost of cleaning = ₹ 14 per m2

So the cost of cleaning 125.714 m2 = ₹ (14 × 125.714)

We get

Cost of cleaning 125.714 m2 = ₹ 1760

Therefore, the cost of cleaning 125.714 m2 is ₹ 1760.

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