Aptitude - Problems on Numbers - Discussion

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 A

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: (Nov 9, 2011)  
Why not it is (a + b + c)^2??

Sai Kumar said: (Oct 7, 2014)  
How to find a, b, c values? If asked in the question?

Yashable said: (Apr 23, 2015)  
And the following three numbers are 8, 7, 5 which is 64+49+25 = 138.

And also 8+7+5 = 20.

Bhupathi said: (Jul 30, 2015)  
Any more easiest method?

Geetha said: (Sep 26, 2015)  
They ask just sum why you take (a+b+c)^2?

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