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Railways PYQCBT 1 2016

RRB NTPC · Question 21

If (a + b + c) = 6 and a^2 + b^2 + c^2 = 14, then (ab + bc + ca) = ?

  1. 22
  2. 11
  3. 33
  4. 44
Show answer & explanation

Answer: (B) 11

Explanation

(a + b + c)² = a² + b² + c² + 2(ab + bc + ca). So 36 = 14 + 2(ab + bc + ca), giving ab + bc + ca = 11.