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Railways PYQCBT 1 2016

RRB NTPC · Question 9

The standard deviation of the set {10, 11, 9, 11, 9} A. 1/√5 B. 2/√5 C. 3/√5 D. 0

  1. B

  2. D

  3. C

  4. A

Show answer & explanation

Answer: (A) B

Explanation

Mean = (10 + 11 + 9 + 11 + 9)/5 = 50/5 = 10. Deviations from the mean are 0, 1, −1, 1, −1, whose squares add to 0 + 1 + 1 + 1 + 1 = 4. Variance = 4/5, so the standard deviation = √(4/5) = 2/√5.