The standard deviation of 100 observations is 10. If 5 is added to each observation and then divided by 20, then what will be the new standard deviation?

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NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. 0.25
  2. 0.5
  3. 0.75
  4. 1.00

Answer (Detailed Solution Below)

Option 2 : 0.5
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Calculation:

Given,

Number of observations, n = 100

Original standard deviation, \( \sigma = 10 \)

Transformation applied to each observation:

New value, \( x' = \frac{x + 5}{20} \)

The additive constant (5) does not affect the standard deviation, and scaling by 20 divides the standard deviation by 20, so the new standard deviation is,

\( \sigma' = \frac{\sigma}{20} \)

\( \sigma' = \frac{10}{20} = 0.5 \)

∴ The new standard deviation is 0.5.

Hence, the correct answer is Option 2.

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