Question

The inner circumference of a circular track $14m$ wide is $440m$. The radius of the outer circle is

• A. $70m$
• B. $56m$
• C. $77m$
• D. $84m$

Answer 1

The correct option is D $84m$

Let $R$ and $r$ be tha radii of the outer and inner circle.

So by given $R-r=14m$

Inner circumference $=2\pi r=2\times \frac{22}{7}\times r=\frac{44r}{7}$
Given $\frac{44r}{7}=440\Rightarrow r=\frac{440\times 7}{44}=70m$

$\therefore$ Radius of outer circle $=70m+14m=84m$