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Q.

If the radii of the circular ends of a frustum of height 6 cm   are 15 cm   and 7 cm  respectively, then what is the volume and lateral surface area (curved surface area) of the frustum [take π=3.14]  ?


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a

2382  cm 3  , 690 cm 2  

b

2382.2  cm 3  , 690.8  cm 2  

c

2002.2  cm 3  , 670.7  cm 2  

d

2364 cm 3  , 580  cm 2   

answer is B.

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Detailed Solution

Given that the radii of the circular ends of a frustum of height 6 cm   are 15 cm   and 7 cm  .
We have the following formulae,
CSA of frustum =π(R+r)l  
Slant height l= h 2 + (Rr) 2  
Volume of frustum = 1 3 πh R 2 + r 2 +Rr   The volume of the frustum will be,
= 1 3 × 22 7 ×6 7 2 + 15 2 +15×7   =6.2857(379) =2382.2  cm 3   l= 6 2 + (8) 2 = 36+64 =10 cm   CSA of frustum will be,
= 22 7 ×(22)×10 =690.8  cm 2  
Thus, the volume is 2382.2  cm 3  and the curved surface area of frustum is 690.8  cm 2  .
Therefore the correct option is 2.
 
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