 Hello and welcome to the session. My name is Asha and I shall be helping you with the following question which says Find the lateral or the curved surface area of a closed cylindrical petrol storage tank that is 4.2 meters in diameter and 4.5 meters high Second we have to find how much steel was actually used if one-twelfth of the steel actually used was wasted in making the tank So let's start with the solution and we are given that diameter of the tank is equal to 4.2 meters Therefore radius of the tank let us denote it by small r is equal to 2.1 meters which we get on dividing the diameter by 2 Also we are given that the height of the tank that is denoted by small h is equal to 4.5 meters and we have to find its curved surface area Now the formula to calculate the curved surface area of a cylinder is equal to 2 pi rh where r is the radius of the cylinder and h is the height of the cylinder So on substituting the values of pi r and h we have 2 into 22 upon 7 into 2.1 meters into 4.5 meters This is further equal to 59.4 meters square So this is the first part that curved surface area of the cylinder is 59.4 meters square Now the second part of the question says how much steel was actually used if one-twelfth of the steel actually used was wasted in making the tank Now to solve the second part first we have to calculate the total surface area of the cylinder which is equal to the curved surface area plus the area of the two bases That is the total surface area of a closed cylinder is equal to the curved surface area that is 2 pi rh plus 2 times the area of the base and base of a cylinder is a circle So we have 2 times of pi r square that is 2 into pi into r taking common h plus r Now let us substitute the values this is equal to 2 into 22 upon 7 and the radius of the cylinder is 2.1 Height of the cylinder is 4.5 meters plus radius is 2.1 meters Therefore simplifying it further we have 2 into 22 7 into 0.3 is 21 so into 0.3 and inside the bracket we have 6.6 And this is equal to 87.12 meters square so this is the total surface area of the closed cylinder because tank Now that is the actual area T used is equal to x meters square and we are given that steel wasted in making of tank is equal to 1 upon 12 of meters square That is x upon 12 meters square now area of steel which is used in making the tank actually is equal to x minus x upon 12 that is 11 upon 12 x So this implies that 11 upon 12 x is equal to the total surface area of the closed cylindrical tank that is 87.12 meters square or x is equal to 87.12 into 12 upon 11 meters square and this is equal to 95.04 meters square Hence our answer is pure sheet of steel actually used in making the closed cylindrical storage petrol tank is 95.04 meters square So this is the answer to the second part and in the first part we have to calculate the curved surface area of the cylindrical tank which is 59.4 meters square So this is the answer to the first part and this completes the session by intake kill