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Q.

The radius and slant height of a cone are in the ratio of 4 : 7. If its curved surface area is 792 cm2, find its radius.

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a

14cm

b

12cm

c

15cm 

d

13cm

answer is B.

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Detailed Solution

Given,
The radius and slant height of a cone are in the ratio of 4 : 7.
Let the radius and slant height be 4x and 7x respectively.
Its curved surface area is 792 cm 2   .
CSA= πrl    Then, π×4x×7x=792  
π×4x×7x=792   22 7 ×4x×7x=792   88 x 2 =792   x 2 = 792 88   x 2 =9   x=3   cm
  x   cannot be negative because x   length cannot be negative.
Therefore, the radius is,
r=4x   r=4×3   r=12   cm
Therefore, the correct option is 2.
 
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