Question

The diameters of two cones are equal. If their slant heights are in the ratio 5:4, then the ratio of their curved surface areas is

• A. 5:4
• B. 16:25
• C. 4:5

Answer 1

The correct option is C 4:5

Given, diameters of two cones are equal.
We know that, diameter = $\frac{radius}{2}$
Implies radii of the two cones are also equal
Given, the slant heights are in the ratio 5:4.
Let the slant height of 1st cone be $l_1$ and slant height of 2nd cone be $l_2$.

Curved surface area of the first cone $=\pi r{l}_1$
Curved surface area of the second cone
$=\pi r{l}_2$

Now, ratio of their curved surface areas
$=\frac{\pi r{l}_1}{\pi r{l}_2}=\frac{l_1}{l_2}=\frac{5}{4}$

So, the ratio of curved surface areas is $5:4$.