Chapter 13 Class 9 Surface Areas and Volumes

Class 9
Important Questions for Exam - Class 9

Learn in your speed, with individual attention - Teachoo Maths 1-on-1 Class

### Transcript

Question 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. [๐ด๐ ๐ ๐ข๐๐ 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 = 2ฯrh = (2ร22/7ร2.1ร4.5) m2 = (2ร22/7ร21/10ร45/10) m2 = (2ร22ร3/10ร45/10) m2 = 59.4 m2 Question 9 Find (ii) How much steel was actually used, if 1/12 of the steel actually used was wasted in making the tank. [๐ด๐ ๐ ๐ข๐๐ ๐= 22/7] h = 4.5 m , r = 2.1 m Total surface area of tank = (2ฯr (r + h)) = 2ร22/7ร2.1ร(2.1+ 4.5) = 2ร22/7ร2.1ร(6.6) = 2ร22/7ร21/10ร66/10 = 87.12 m2 Let Amount of steel used in making the tank = x Steel wasted = ๐ฅ/12 Given that Amount of steel required โ Amount of steel wasted = TSA of tank x โ ๐ฅ/12 = 87.12 11/12 ๐ฅ = 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.

#### Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.