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

• Mensuration (C10)

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.

Solution

Here, l = 4 cm

2πr₁ = 18 cm

2πr₂ = 6 cm

πr₁ = 9, πr₂ = 3

Curved surface area of frustum = π(r₁ + r₂) × l

= (πr₁ + πr₂) × l

= (9 + 3) × 4

= 48 cm²