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Ex 13.2, 9 - Find (i) The lateral or curved surface area - Area Of Cylinder

  1. Chapter 13 Class 9 Surface Areas and Volumes
  2. Serial order wise
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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. [π΄π‘ π‘ π‘’π‘šπ‘’ πœ‹= 22/7] Height (h) of cylindrical tank = 4.5 m Radius (r) of the circular end of cylindrical tank =Β (4.2/2) m = 2.1 m Curved Surface Area of tank = 2Ο€rh = (2Γ—22/7Γ—2.1Γ—4.5) m2 = (2Γ—22/7Γ—21/10Γ—45/10) m2 = (2Γ—22Γ—3/10Γ—45/10) m2 = 59.4 m2 Ex 13.2, 9 Find (ii) How much steel was actually used, ifΒ  1/12 of the steel actually used was wasted in making the tank.Β  [π΄π‘ π‘ π‘’π‘šπ‘’ πœ‹= 22/7] h = 4.5 m , r = 2.1 m Total surface area of tank = (2Ο€rΒ (r + h)) = 2Γ—22/7Γ—2.1Γ—(2.1+ 4.5) = 2Γ—22/7Γ—2.1Γ—(6.6) = 2Γ—22/7Γ—21/10Γ—66/10 = 87.12 m2 Let Amount of steel used in making the tank = x Steel wasted = π‘₯/12 Given that Amount of steel required – Amount of steel wasted = TSA of tank x – π‘₯/12 = 87.12 11/12 π‘₯ = 87.12 x = 12/11 Γ— 87.12 x = 95.04 m2 Therefore, 95.04 m2Β steel was used in actual while making such a tank.

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