Question

A running track is the ring formed by two concentric circles. It is $10m$ wide. The circumferences of the two circle differ by about.

• A. $10m$
• B. $30m$
• C. $60m$
• D. $100m$
• E. None of these

Answer 1

Answer: (C)

$60m$

Since, $C_1$ & $C_2$ are two concentric circles with radii $r_1$ & $r_2=r_1+10$

So, circumference of both the circles, $C_1=2\pi r_1,C_2=2\pi (r_1+10)$

$\therefore C_2-C_1=20\pi \sim 60\left(m\right)$.