Momina AbdulQadir G.

asked • 06/15/18

The diameter of circle A is the same as the radius of circle B. If the sum of their circumferences is 81pi. What is the diameter of circle B?

Circumference = 2 pi r
 

1 Expert Answer

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Philip P. answered • 06/15/18

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Let r = the radius of circle A.  The radius of circle B is twice as big (2r).  Their circumferences are:
 
CA = 2 pi r
CB = 2 pi 2r = 4 pi r
 
CA + CB = 2 pi r +4 pi r
81 pi =  6 pi r
 
Solve for r.  The diameter of circle B is 2(2r) = 4r.
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Momina AbdulQadir G.

Thank you sir. But the choices of this question I have been given are 12, 24, 6.....Please explain how that ans is possible. 
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06/15/18

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