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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

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

Grade:10

3 Answers

Vasanth SR
askIITians Faculty 1335 Points
6 years ago
Please enclose the proper supporting document
Subhiksha
11 Points
6 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.
 
\prodr2 = 616
      r2 = 616 x 7/22
      r  =  14cm.
 
Therefore radius of innercircle = 14cm.
amisha
31 Points
6 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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