Multiple choice

The sum of the squares of three positive numbers is 138, while the sum of their products taken two at a time is 131. Their sum is

  1. 20

  2. 30

  3. 40

  4. 50

  5. None of these
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A Correct answer
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) = 20

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