the circumference of two concentric circles forming a ring are 88 cm..., Area, General Mathematics

Question:The circumference of two concentric circles forming a ring are 88 cm and 66 cm respectively. The width of the ring is :

A `3.5 cm` 
B `10.5 cm` 
C `7 cm` 
D `14 cm`

/98

+ AnswerA

+ ExplanationLet, inner radius = r & outer radius = R cm.

Then,` 2 xx 22/7 xx R = 88 => R`

      `= (88 xx 7/44)`

     `= 14 cm.`

   ` 2 xx 22/7 xx r = 66 => r`

  `= (66 xx 7/44)`

 `= 21/2 cm`

`= 10.5 cm.`

:. width of the ring 

`= (14 - 10.5) cm`

`= 3.5 cm.`

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