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

Question 7 Volume And Surface Area Of Solids Exercise 15C

A bus stop is barricaded from the remaining part of the road by using 50 hollow cones made of recycled cardboard. Each one has a base diameter of 40cm and height 1m. If the outer side of each of the cones is to be painted and the cost of painting is ₹ 25 per m2, what will be the cost of painting all these cones? (Use π = 3.14 and √1.04 = 1.02.)

It is given that

Radius of the cone = 20cm = 0.2m

Height of the cone = 1m

We know that

Slant height l = √ (r2 + h2)

By substituting the values

l = √ (0.22 + 12)

On further calculation

l = √ (0.04 + 1) = √ 1.04

So we get

l = 1.02m

We know that

The curved surface area of cone = πrl

By substituting the values

Curved surface area of cone = 3.14 × 0.2 × 1.02

On further calculation

The curved surface area of cone = 0.64056 m2

So, the curved surface area of 50 cones = 50 × 0.64056 = 32.028 m2

It is given that

The cost of painting = ₹ 25 per m2

So the cost of painting 32.028 m2 area = ₹ 25 × 32.028 = ₹ 800.70

Therefore, the cost of painting all of these cones is ₹ 800.70.

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