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Aptitude - Problems on Numbers - Discussion

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"Hold a true friend with both hands."
- (Proverb)
7. 

The sum of the squares of three numbers is 138, while the sum of their products taken two at a time is 131. Their sum is:

[A]. 20[B]. 30
[C]. 40[D]. None of these

Answer: Option

Explanation:

Let the numbers be a, b and c.

Then, a2 + b2 + c2 = 138 and (ab + bc + ca) = 131.

(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca) = 138 + 2 x 131 = 400.

(a + b + c) = 400 = 20.


Kailash said: (Wed, Nov 9, 2011 08:45:58 PM)    
 
Why not it is (a + b + c)^2??

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