Question

The area of the ring between two concentric circles is $3168{cm}^2$. Find the radii of the two circles if (i) their sum is $42cm$ and (ii) their difference is $28cm$.

Answer 1

Let two radius are 'x' and 'y', so,

$x+y=\mathrm{42....}\left(1\right)$

and

$x-y=\mathrm{28.....}\left(2\right)$

Now adding (1) and (2), we get

$2x=70$

$x=35$

Putting in (1)

$35+y=42$

$y=7$

Therefore, radius of two concentric circles are 35 cm and 7 cm.