# A circle has an area of M cm^2 and a circumference of N cm. If M/N=20, what is the radius of the circle in cm?

Aug 1, 2015

color(blue)(r = 40cm

#### Explanation:

The formula for the area of a circle is color(blue)(pir^2
The formula for the circumference of a circle is color(blue)(2pir

The area given is : $M c {m}^{2}$

The circumference given is $N c m$

$\frac{M}{N} = \textcolor{b l u e}{\frac{\pi {r}^{2}}{2 \pi r}} = 20$

$\textcolor{b l u e}{\frac{\cancel{\pi} {r}^{2}}{2 \cancel{\pi} r}} = 20$

$\frac{r}{2} = 20$

color(blue)(r = 40cm