Q19 of 47 Page 1

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.

we know


Curved surface area of frustum of a cone = πl(r1 + r2)


Where, l = slant height, r1 and r2 are radii (r1 > r2)


For given frustum,


Perimeter of circular end with radius r1 = 18 cm


[As perimeter of circle = circumference of circle = 2πr]


⇒ 2πr1 = 18



Perimeter of circular end with radius r2 = 6 cm


[As perimeter of circle = circumference of circle = 2πr]


⇒ 2πr2 = 6



Slant height, l = 4 cm


Therefore,


Curved surface area


⇒ Curved Surface area = 48 cm2


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