# Areas Related To Circles

#### Answer:

It is given that, and

We know that the circumference C of semicircle of radius be *r* is

$C=\mathrm{\pi}r$

The inside perimeter of running track is the sum of twice the length of straight portion and circumferences of semicircles. So,

inside perimeter of running track = 400 *m*

$2l+2\mathrm{\pi}r\mathit{=}400m$

$\Rightarrow 2\times 90+2\times \frac{22}{7}\times r=400m$

$\Rightarrow r=\frac{220\times 7}{2\times 22}=35m$

Thus, radius of inner semicircle is 35 m.

Now,

radius of outer semi circle *r*' = 35 + 1…

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