Maths-
General
Easy
Question
The area enclosed between two concentric circles is 770 cm2. If the radius of the outer circle is 21cm, calculate the radius of inner circle
Hint:
Area enclosed between two concentric circles is the difference of the areas of two circles
The correct answer is: 14 cm
It is given that radius of outer circle, r1 = 21 cm
Let radius of inner circle = r
Area enclosed between two concentric circles = 770 cm2.
Area of outer circle – Area of inner circle = 770 cm2.
(r1)2 - r2 = 770
× (21)2 - × (r)2 = 770
× (212 – r2 ) = 770
441 – r2 = 245
r2 = 441 – 245 = 196
r = 14 cm
Hence, radius of inner circle is 14 cm.
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