# 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.)

**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.).