Q18 of 35 Page 311

Buying a bangle from fair Nila wears in her hand. The Bangle contains 269.5 sq. cm. metal. If the length of outer diameter of bangle is 28 cm, let us write by calculating the length of inner diameter.



The bangle is like two concentric circles.


Given: Area of the bangle = 269.5 cm2


Outer diameter of bangle = 28 cm


⇒ Outer radius = 14 cm


Area of the bangle = Area of the larger circle – area of the smaller circle


∵The area of a circle = πr2


⇒ Area of the bangle = πR2 - πr2





⇒ 196 - r2 = 85.75


⇒ r2 = 110.25


⇒ r = 10.5


Inner radius = 10.5 cm


⇒ Inner diameter = 2× 10.5 = 21 cm


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