The ratio of the outer and inner perimeters of a circular path is 23 : 22. If the path is 5 metres wide, the diameter of the inner circle is
(a) 55 m
(b) 110 m
(c) 220 m
(d) 230 m
Let OA = r be the radius of the inner circle and OB = r′ be the radius of the outer circle.
Therefore, circumference of the inner circle $=2 \pi r$ and circumference of the outer circle $=2 \pi r^{\prime}$
Here we have to find the diameter of the inner circle.
We have given the ratio of outer and inner perimeters of a circular path.
$\therefore \frac{2 \pi r^{\prime}}{2 \pi r}=\frac{23}{22}$
Simplifying the above equation we get,
$\frac{r^{\prime}}{r}=\frac{23}{22}$
$\therefore 22 r^{\prime}=23 r$
$\therefore 22 r^{\prime}-23 r=0$....(1)
We have also given that the path is 5 meters wide, that is we have given
$r^{\prime}-r=5 \ldots \ldots .(2)$
We are asked to find the diameter of the inner circle hence, we will eliminate r′ using equations (1) and (2) for that we will multiply equation (2) by 22.
$22 r^{\prime}-22 r=110 \ldots \ldots \ldots(3)$
Subtracting equation (1) from equation (3) we get, $r=110$
Therefore, radius of the inner circle is 110 meters.
Therefore, diameter of the inner circle $=2 \times 110=220$ meters
Therefore, diameter of the inner circle is 220 meters.
Hence, the correct answer is option (c).