Question:

The standard deviation of a distribution is 5. If each observation is increased by 2, then the new standard deviation will be:

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Adding or subtracting a constant changes only the mean. Multiplying every observation by a constant \(k\) changes the standard deviation to \[ |k|\sigma. \]
  • 5
  • 7
  • 3
  • 10
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The Correct Option is A

Solution and Explanation

Concept: Standard deviation measures the spread of observations around their mean. A very important property is: \[ \sigma(X+k)=\sigma(X), \] where \(k\) is any constant. Thus, adding or subtracting a constant changes the mean but does not change the standard deviation.

Step 1:
Determine the given information. Original standard deviation: \[ \sigma=5. \] Each observation is increased by \[ 2. \]

Step 2:
Apply the property of standard deviation. Since adding a constant does not affect dispersion, \[ \text{New Standard Deviation} = \text{Old Standard Deviation}. \] Therefore, \[ \sigma_{\text{new}} = 5. \] Conclusion: \[ \boxed{5} \] Hence, the correct answer is Option (A).
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