Aptitude  Problems on Numbers  Discussion




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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, a^{2} + b^{2} + c^{2} = 138 and (ab + bc + ca) = 131.
(a + b + c)^{2} = a^{2} + b^{2} + c^{2} + 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?? 
Sai Kumar said:
(Tue, Oct 7, 2014 04:49:50 PM)



How to find a, b, c values? If asked in the question? 
Yashable said:
(Thu, Apr 23, 2015 09:21:44 PM)



And the following three numbers are 8, 7, 5 which is 64+49+25 = 138.
And also 8+7+5 = 20. 
Bhupathi said:
(Thu, Jul 30, 2015 12:40:01 PM)



Any more easiest method? 
Geetha said:
(Sat, Sep 26, 2015 12:52:44 PM)



They ask just sum why you take (a+b+c)^2? 

