Question

Area enclosed between concentric circkes is 770 and the radius of outer circle is 21. Find the radius of the inner circle

Answer 1

Answer:

Radius of inner circle = 14 cm

Step-by-step explanation:

Area enclosed between 2 concentric circles = 770 cm²

Area Enclosed = Area of Outer Circle - Area of Inner Circle.

Also it is given that,

Radius of Outer circle = 21 cm

⇒ Area of Outer Circle = πR² = 22/7 × 21 × 21 = 1386 cm²

⇒ Area Enclosed = πR² - πr²

Here, R is the radius of outer circle and r is the radius of inner circle.

⇒ 770 cm² = 1386 cm² - πr²

⇒ πr² = 1386 - 770 = 616 cm²

⇒ r² = 616 / π

⇒ r² = 616 × 7 / 22 = 196 cm²

⇒ r = √196 = 14 cm

Hence the radius of inner circle is 14 cm.