# A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. Each cone has a base diameter of 40 cm and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is ₹ 12 per m^{2}, what will be the cost of painting all these cones? (Use π = 3.14 and take √1.04 = 1.02)

**Solution:**

Given: The base diameter of the cone is 40 cm and its height is 1m.

Since the outer side of each cone is to be painted, the area to be painted will be equal to the curved surface area of the cone.

The curved surface area of a right circular cone with base radius(r) and slant height(l) is πrl

Slant height, l = √(r² + h²) where h is the height of the cone.

Diameter, d = 40cm = 40/100 m = 0.4m

Radius, r = 0.4/2m = 0.2m

Height, h = 1 m

Slant height, l = √(0.2)² + (1)²

= √0.04m² + 1m²

= √1.04 = 1.02m (given)

The curved surface area = πrl

= 3.14 × 0.2m × 1.02m

= 0.64056 m^{2}

Curved surface area of 50 cones = 50 × 0.64056 m^{2} = 32.028 m^{2}

Cost of painting of 50 cones at ₹ 12 per m^{2} = 32.028 × 12

= ₹ 384.34 (approx.)

Thus, the cost of painting all the cones is ₹ 384.34 (approx.)

**☛ Check: **NCERT Solutions Class 9 Maths Chapter 13

**Video Solution:**

## A bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. Each cone has a base diameter of 40 cm and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is ₹ 12 per m², what will be the cost of painting all these cones? (Use π = 3.14 and take √1.04 = 1.02)

Class 9 Maths NCERT Solutions Chapter 13 Exercise 13.3 Question 8

**Summary:**

It is given that a bus stop is barricaded from the remaining part of the road, by using 50 hollow cones made of recycled cardboard. Each cone has a base diameter of 40 cm and a height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is ₹ 12 per m², the cost of painting all these cones is ₹ 384.34 (approx.).

**☛ Related Questions:**

- A conical tent is 10 m high and the radius of its base is 24 m. Find i) Slant height of the tent. ii) Cost of the canvas required to make the tent, if the cost of 1 m² canvas is ₹ 70.
- What length of tarpaulin 3 m wide will be required to make conical tent of height 8 m and base radius 6 m? Assume that the extra length of material that will be required for stitching margins and wastage in cutting is approximately 20 cm (Use π = 3.14)
- The slant height and base diameter of a conical tomb are 25 m and 14 m respectively. Find the cost of white washing its curved surface at the rate of ₹210 per 100 m².
- A joker’s cap is in the form of a right circular cone of base radius 7cm and height 24cm. Find the area of the sheet required to make 10 such caps.

visual curriculum