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:

Question: 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.

Video Explanation: https://youtu.be/qmJ-0X8j_xQ