Question

Circumference of the base of the cone is $154cm$. Its slant height is $7cm$. Curved surface area of the cone is:

• A. $343$ sq cm
• B. $308$ sq cm
• C. $1078$ sq cm
• D. $539$ sq cm

Answer 1

The correct option is D $539$ sq cm

Let the radius of the base of the cone be $r$ cm .

Now circumference of base $=154$cm.

$⟹$ $2\pi r=154$

$⟹$$r=\frac{154\times 7}{2\times 22}=\frac{49}{2}cm$.

Also, Slant height $=7$cm.

We know, curved area of cone $=\pi rl$.

$=\frac{22}{7}\times \frac{49}{2}\times 7=539c{m}^2$.

Therefore, option $D$ is correct.