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Q.

Volume of a hollow sphere is 113527cm3 . If the outer radius is 8 cm, find the inner radius of the sphere. (Take π=227 )


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a

5 cm

b

8 cm

c

9 cm

d

3 cm 

answer is A.

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Detailed Solution

Let's say that the inside radius of the hollow sphere is x cm and the outside radius is y=8 cm
Question Image.
 Using the formula V= 43πr3 , the volume of the outside sphere is 43π83  and the volume of the inside sphere is 43πx3  .
The volume of the hollow sphere (shaded part) will be 43π83-43πx3  . .
According to the question:
  43π83-43πx3  = 113527
Taking out the common factors  43π and using π=227 , we get:
 43×227×(83-x3)= 113527
⇒(83-x3) =)= 113527×)= 722× 34
Note that 11352 is multiple of 11, because (1+3+2)−(1+5)=6−6=0. Dividing 11352 by 22 and cancelling out the 7's, we get:
 512−x3=516× 34
 512−x3 =129×3
 512−x3 =387
 x3 =512−387
 x3 =125
Since, 5×5×5=125, we get:
 x=5.
∴ The inner radius of the sphere is 5 cm.
 
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