 Hi and welcome to the session. Let us discuss the following question. Question says the slant height of a frustum of a cone is 4 cm and the perimeters of its circular ends are 18 cm and 6 cm. Find the curved surface area of the frustum. First of all let us understand that curved surface area of a frustum of a cone is equal to pi multiplied by l multiplied by r1 plus r2 where l is the slant height and r1 and r2 are radii of the two circular ends. Now we will use this formula as our key idea to solve the given question. Let us now start with the solution. Now we are given that slant height of the frustum of a cone is equal to 4 cm. So we can write slant height that is l is equal to 4 cm. Now we are given that perimeters of two circular ends are 18 cm and 6 cm. Now let us assume that r1 and r2 are radii of two circular ends of the given frustum. We are given perimeter of this circular end is equal to 6 cm. Now we know perimeter of the circle is equal to circumference of the circle. So we can write 2 pi r1 is equal to 6 cm and here we are given that perimeter of this circular end is equal to 18 cm. So we can write circumference of this circular end that is 2 pi r2 is equal to 18 cm. We know circumference of a circle is equal to 2 pi multiplied by radius of the circle. Now we get 2 pi r1 is equal to 6 cm or we can say r1 is equal to 6 upon 2 pi cm. We also know that 2 pi r2 is equal to 18 cm. Now this further implies r2 is equal to 18 upon 2 pi cm. Now we have to find curved surface area of frustum. From key idea we know curved surface area of frustum is equal to pi l multiplied by r1 plus r2 where l is the slant height of the frustum and r1 and r2 are radii of two circular ends of the frustum. Now substituting corresponding values of l r1 and r2 in this expression we get pi multiplied by 4 multiplied by 6 upon 2 pi plus 18 upon 2 pi cm2. Now this expression is further equal to 4 pi multiplied by 6 plus 18 upon 2 pi cm2. Now this is further equal to 4 pi multiplied by 24 upon 2 pi cm2. We know 6 plus 18 is equal to 24. Now we will cancel common factor 2 pi from numerator and denominator both and we get 48 cm2 is equal to curved surface area of the frustum. So our required answer is curved surface area of the frustum is equal to 48 cm2. This completes the session. Hope you understood the solution. Take care and keep smiling.