Last updated at May 29, 2018 by Teachoo

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Ex 13.2, 9 Find The lateral or curved surface area of a closed cylindrical petrol storage tank that is 4.2 m in diameter and 4.5 m high. [๐ด๐ ๐ ๐ข๐๐ ๐= 22/7] Height (h) of cylindrical tank = 4.5 m Radius (r) of the circular end of cylindrical tank = (4.2/2) m = 2.1 m Curved Surface Area of tank = 2ฯrh = (2ร22/7ร2.1ร4.5) m2 = (2ร22/7ร21/10ร45/10) m2 = (2ร22ร3/10ร45/10) m2 = 59.4 m2 Ex 13.2, 9 Find (ii) How much steel was actually used, if 1/12 of the steel actually used was wasted in making the tank. [๐ด๐ ๐ ๐ข๐๐ ๐= 22/7] h = 4.5 m , r = 2.1 m Total surface area of tank = (2ฯr (r + h)) = 2ร22/7ร2.1ร(2.1+ 4.5) = 2ร22/7ร2.1ร(6.6) = 2ร22/7ร21/10ร66/10 = 87.12 m2 Let Amount of steel used in making the tank = x Steel wasted = ๐ฅ/12 Given that Amount of steel required โ Amount of steel wasted = TSA of tank x โ ๐ฅ/12 = 87.12 11/12 ๐ฅ = 87.12 x = 12/11 ร 87.12 x = 95.04 m2 Therefore, 95.04 m2 steel was used in actual while making such a tank.

Chapter 13 Class 9 Surface Areas and Volumes

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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.