Question

The surface area of a football is $616{mm}^2.$ Calculate its radius.

• A. $4mm$
• B. $7mm$
• C. $6mm$
• D. $5mm$

Answer 1

The correct option is B $7mm$

Let the radius of the football be $r.$ then its surface area will be $4\pi r^2.$

But it is given that, the surface area of football is equal to $616m{m}^2.$

Hence,

$616=4\pi r^2$
$\Rightarrow 616=4\times \frac{22}{7}\times r^2$
$\Rightarrow \frac{(616\times 7)}{(4\times 22)}=r^2$
$\Rightarrow \frac{4312}{88}=r^2$
$\Rightarrow 49=r^2$
$\Rightarrow r=7mm$

Therefore, option $B$ is correct.