Last updated at May 29, 2018 by Teachoo

Transcript

Example 10 A hemispherical dome of a building needs to be painted . If the circumference of the base of the dome is 17.6 m, find the cost of painting it, given the cost of painting is Rs 5 per 100 cm2. Since only the rounded surface of the dome is to be painted, we would need to find the curved surface area of the hemisphere Let radius of dome be r Circumference of dome = Circumference of circle with radius r 17.6 = 2πr 17.6 = 2 × 22/7 × r 17.6 × 7/(2 × 22) = r r = 17.6 × 7/(2 × 22) m r = 2.8 m r = 2.8 × 100 cm r = 280 cm The curved surface area of the dome = 2πr2 = 2 ×22/7 × (280) × (280) cm2 = 2 × 22 × (40) × (280) cm2 = 492800 cm2 Now, cost of painting 100 cm2 = Rs 5. Cost of painting 1 cm2 = Rs 5 × 1/100 Cost of painting 492800 cm2 = Rs 5 × 1/100 × 492800 = Rs 24640 Cost of painting the dome is Rs 24,640

Examples

Chapter 13 Class 9 Surface Areas and Volumes

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About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 10 years. He provides courses for Maths and Science at Teachoo.