Two concentric circles form a ring. If the inner and outer circumferences of the ring are 20π cm and 40π cm respectively, then the width of the ring is ___.
A
10 cm
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B
20 cm
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C
30 cm
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D
40 cm
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Solution
The correct option is A 10 cm We know that the circumference of a circle of radius r units is given by 2πr units. Inner circumference of the ring = 20π cm ⇒ Radius of the inner circle in the ring = 20π2π cm=10 cm Outer circumference of the ring = 40π cm ⇒ Radius of the outer circle in the ring = 40π2π cm=20 cm Now, width of the circular ring equals the difference in the outer and inner radii. ∴ Width of the circular ring = 20 cm−10 cm=10 cm