Maths-
General
Easy

Question

The area enclosed by the circumference of two concentric circles is 364.5 cm2. If the circumference of the inner circle is 88cm, calculate the radius of the outer circle.

hintHint:

Area enclosed by the circumference of two concentric circles is the difference of the areas of two circles.

The correct answer is: 17.66 cm


    It is given that Circumference of inner circle = 88 cm
    straight pi r =  88
    2 × 22 over 7 ×  r  =  8
    r  =  14 cm
    Let radius of outer circle = r1
    Area enclosed by the circumference of two concentric circles = 364.5 cm2
    i.e. Area of outer circle – Area of inner circle = 364.5 cm2
    straight pi (r1)2  - straight pi r2     = 364.5
    22 over 7 × (r1)2  - 22 over 7 × (14)2  = 364.5
    22 over 7((r1)2 – 142) = 364.5
    ((r1)2 – 142   = fraction numerator 2551.5 over denominator 22 end fraction
    (r1)2 = 311.977
    r1  = 17.66 cm

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