The larger diameter of a frustum cone is thrice the smaller radius which is $4\ cm$. The slant height of the cone is $13\ cm$. What is the curved surface area? $(Use\ \pi=3.14)$.

Given: The larger diameter of a frustum cone is thrice the smaller radius which is $4\ cm$. The slant height of the cone is $13\ cm$.

To do: To find the surface area of the frustum cone.

Solution:

As given, slant height of the cone $l=13\ cm$, smaller radius $r=4\ cm$

$\therefore$ Larger diameter $d=3\times 4=12\ cm$

$\Rightarrow$ Larger radius $R=\frac{d}{2}=\frac{12}{2}=6\ cm$

$\therefore$ Curved surface area of the frustum$=\pi ( r+R)l$

$=\frac{22}{7}\times( 4+6)\times 13$

$=408.2\ cm^2$ 

Thus, the curved surface area of the frustum is $408.2\ cm^2$.

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Updated on: 10-Oct-2022

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