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The standard error of sample mean based on 100 observations from normal distribution with mean 50 and standard deviation 5 is ............ .

  • A.\(\dfrac{1}{2}\)
  • B.\(\dfrac{1}{100}\)
  • C.\(\dfrac{1}{20}\)
  • D.\(\dfrac{1}{\sqrt{2}}\)

Answer: A

The standard error is 1/2.

The standard error of the mean is the population standard deviation divided by the square root of the sample size:

\[ \begin{aligned} SE(\bar{x}) &= \frac{\sigma}{\sqrt{n}} = \frac{5}{\sqrt{100}} \\ &= \frac{5}{10} = \frac{1}{2} \end{aligned} \]

The mean of 50 plays no part. 1/20 is what you get by dividing 5 by n instead of by its square root, and 1/100 and \(1/\sqrt{2}\) do not follow from the formula at all.

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