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  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

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    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) = \(\sqrt{400}\)= 20.

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