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in the adjoining figure the area enclosed between the concentric circles is 770 cm2 if the radius of the outer circle is 21 cm calculate the radius of inner. circle

jahanavi singh , 8 Years ago
Grade 10
anser 3 Answers
Vasanth SR

Last Activity: 7 Years ago

Please enclose the proper supporting document

Subhiksha

Last Activity: 7 Years ago

Given :
Radius of outer circle = 21cm.
Area between inner & outer circle = 770cm2.
 
Area of outer circle = \prodr2
                                     = 22/7 x 212
                                     = 1386cm2.
 
Area of innercircle = 1386-770
                              = 616cm2.
 
\prodr= 616
      r= 616 x 7/22
      r  =  14cm.
 
Therefore radius of innercircle = 14cm.

amisha

Last Activity: 7 Years ago

here we have
the radius of outer circle= 21cm
area between the concentric circle =7702 
\prodR2 = 22/7*21*21
           =1386cm 
\prodr2  =1386cm -770cm
          = 616cm
so,
radius of inner circle 
\prodr2 = 22/7*r2
616 =22/7*r2
616*7/22 = r2
196 = r2
142 = r2
14 = r
hence radius = 14 cm 

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