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### Discussion :: Problems on Numbers

1. 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:

2. A.

20

B.

30

C.

40

D.
 None of these

Explanation :

Let the numbers be ab 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) = $$\sqrt{400}$$= 20.

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