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Question
The areas of two concentric circles are 1386 cm2 and 962.5 cm2. The width of the ring is
Options
2.8 cm
3.5 cm
4.2 cm
3.8 cm
Solution
3.5 cm
Let r cm and R cm be the radii of two concentric circles.
Thus, we have:
πR2 = 1386
`=> 22/7xx"R"^2 = 1386`
`rArr "R" = (1386xx7/22) "cm"^2`
⇒ R2 = 441 cm2
⇒ R = 21 cm
Also,
πr2 = 962.2
`=> 22/7xx"r"^2 = 962.2`
`⇒ r2 = (962.2 × 7/22) "cm"^2`
`=> "r"^2 = (962.2/10xx7/22)"cm"^2`
`=>"r"^2 =1225/4 "cm"^2`
`=> "r" = 35/2 "cm"`
∴ Width of the ring = (R - r)
`= (21 - 35/2) "cm"`
`= 7/2 "cm"`
= 3.5 cm
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