RD Sharma - Mathematics

Book: RD Sharma - Mathematics

Chapter: 20. Surface Area and Volume of a Right Circular Cone

Subject: Mathematics - Class 9th

Q. No. 22 of Exercise 20.1

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A bus stop is barricaded from the remaining part of the road, by using 50 hollow cone made of recycled card-board. 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 Rs. 12 per m2. What will be the cost of painting all these cones. (Use π=3.14 and = 1.02).

We have,

Radius of base= 20 cm = 0.2 m

Height of cone = 1 m

slant height l = = m = m

= 1.02 m

Curved surface area of a cone = πrl =3.14×0.2×1.02 m2

Cost of painting = Rs. [(3.14×0.2×1.02×12)×50] = Rs. 384.33

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