Question

One circle has radius of $98cm$ and a second concentric circle has a radius of $1m26cm$. How much longer is the circumference of the second circle than that of the first?

Answer 1

Let $OA=r=98cm$ and $OB=R=1m26cm$

Now, we know that $1m=100cm$

Hence, $R=100+26=126cm$

Now we know that circumference of circle is given by $2\pi r$

Since, $R>r$, therefore, $2\pi R>2\pi r$

Therefore, difference between the outer circumference and the inner circumference,

$=2\pi R-2\pi r$

$=2\pi (R-r)$

$=2\times \frac{22}{7}\times (126-98)$

$=2\times \frac{22}{7}\times 28$

$=176cm$

Hence, the circumference of the second circle is $176cm$ longer than that of the first circle.