College of Admission Tests Multan

Number System

Solve the question of and select the option from the choices A through D/E. Check your Answer and view the explanation.

Question: 4

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
  • 15
  • 20
  • 25
  • 35

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Correct Answer: B

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)
(a + b + c)2 = 138 + 2 x 131 = 400
(a+b+c)2 = 400
(a + b + c) = 400 =20.