# Aptitude - Problems on Numbers - Discussion

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"Everything you can imagine is real."
- Pablo Picasso
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

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??

 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?