the areas of two concentric circles forming a ring are 154 sq..., Area, General Mathematics

Question:The areas of two concentric circles forming a ring are 154 sq. and 616 sq.cm. The breadth of the ring is :

A `7 cm` 
B `14 cm` 
C `21 cm` 
D `28 cm`

/98

+ AnswerA

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

Then,`22/7 xx r^2 = 154 or r^2`

`= (154 xx 7/22).` So, r = 7.

Also,` 22/7 xx R^2 = 616 or R^2`

`= (616 xx 7/22) or R = 14`

:. Breadth of the ring

`= (R - r) = (14 - 7) = 7 cm.`

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