Question

What is the diameter of a circle whose area is equal to the sum of the areas two circles of radii $40cm$ and $9cm$?

Answer 1

Area of the circle $=$ sum of area of two circles

$\pi R^2=\pi \times {40}^2+\pi \times 9^2$

$\Rightarrow R^2=1600+81=1681$

$\therefore R=\sqrt{1681}=41$cm

$\therefore$ Diameter of given circle$=41\times 2=82$cm