Question

A race track is in the form of a ring whose inner circumference is $352m$, and the outer circumference is $396m$. Find the width of the track.

• A. $5m$
• B. $8m$
• C. $6m$
• D. $7m$

Answer 1

The correct option is D $7m$

Let the outer and inner radii of the ring be R metres and r metres respectively.
Then, $2\pi R=396$ and $2\pi r=352$
$\Rightarrow 2\times \frac{22}{7}\times R=396$ and $2\times \frac{22}{7}\times r=352$
$\Rightarrow R=396\times \frac{7}{22}\times \frac{1}{2}$ and $r=362\times \frac{7}{22}\times \frac{1}{2}$
$\Rightarrow R=63m$ and $r=56m$
Hence, width of the track $=(R-r)m$
$=(63-56)m=7m$