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NDA 2018 Maths · Mathematics · Statistics · easy

The standard deviation of the observations 4,8,12,16,20 is

Single correct option

The standard deviation of the observations 4,8,12,16,204,8,12,16,20 is
  1. A. 3232
  2. B. 88
  3. C. 40\sqrt{40}
  4. D. 424\sqrt2
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Answer: (D) 424\sqrt2

The mean is 12 and the squared deviations are 64,16,0,16,6464,16,0,16,64, summing to 160. Variance =1605=32=\frac{160}{5}=32, so the standard deviation is 32=42\sqrt{32}=4\sqrt2. The value 32 is the variance, and 40\sqrt{40} divides by 4 instead of 5.
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Original question written in the NDA 2018 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake