Question

The diameter of a circle is $42cm$, Find its perimeter. If the perimeter of the circle is doubled, what be the radius of the new circle $(\text{Take}\pi =\frac{22}{7})$.

Answer 1

Finding the perimeter of circle

Given: Diameter $=42cm$.

$\therefore$ Diameter of circle $=2r=42cm$

$\Rightarrow r=\frac{42}{2}=21cm$

Perimeter of circle $=2\pi r$

$=2\times \frac{22}{7}\times 21$

$=2\times 22\times 3=132cm$.

Finding the radius of new circle

Now, if perimeter of circle is doubled then new perimeter $\left(P^{\prime }\right)$ will be equal to,

$P^{\prime }=2\times 132=264cm$

$\Rightarrow$ Radius $=\frac{264}{2\pi }=\frac{264}{1}\times \frac{7}{22}\times \frac{1}{2}$

$\therefore$ Radius $=42cm$

Hence, the perimeter of circle is $132cm$ and radius of new circle is $42cm$.