Question

The area of the circular ring enclosed between two concentric circles is 88 cm². Find the radii of the two circles, if their difference is 1 cm.

Answer 1

Let the radius of outer circle = R cm
And, the radius of inner circle = r cm
Then, we have
R - r = 1     ....(i)
And, π(R² -  r²) = 88
⇒ (R - r)(R + r) 

= `88 xx (7)/(22)`
⇒ 1 x (R + r) = 28
⇒ R + r = 28   ....(ii)
Adding (i) and (ii), we get
2R = 29
⇒ R = 14.5cm
Now, R + r = 28
⇒ 14.5 + r = 28
⇒ r = 13.5cm.