Question

The slant height of a frustum of a cone is 4 cm and the perimeters (circumference) of its circular ends are 18 cm and 6 cm. Find the curved surface area of the frustum(in $c{m}^2$).

• A. $56c{m}^2$
• B. $40c{m}^2$
• C. $52c{m}^2$
• D. $48c{m}^2$

Answer 1

The correct option is D

$48c{m}^2$

Slant height of a frustum of a cone =
l = 4 cm
Perimeter of its first circular end =
18 cm
Perimeter of its second circular end =
6 cm

Curved Surface Area of frustum of the cone

$=\pi .(r_1+r_2)l$

$=(\pi .r_1+\pi .r_2)l$

$=(2\pi .r_1+2\pi .r_2)\frac{l}{2}$

$=(18+6)\frac{4}{2}=48c{m}^2$