Question

A frustum of a right circular cone of height $16\text{cm}$ with radii of its circular ends as $8\text{cm}$ and $20\text{cm}$ has its slant height equal to:

• A. $18\text{cm}$
• B. $16\text{cm}$
• C. $20\text{cm}$
• D. $24\text{cm}$

Answer 1

The correct option is C $20\text{cm}$

Given:

$H=16\text{cm}$

$R=20\text{cm}$

$r=8\text{cm}$

Let the slant height of the frustum of cone be $l$,

$\begin{array}{cc}l& =\sqrt{h^2+{(R-r)}^2}\\ & =\sqrt{{\left(16\right)}^2+{(20-8)}^2}\\ & =\sqrt{256+144}\\ & =\sqrt{400}\\ & =20\text{cm}\end{array}$