Question
For a normal distribution the estimated value of quartile deviation is $12.$ Find the value of its standard deviation.

Answer

Here, quartile deviation $=12$
In normal distribution,
Estimated value of quartile deviation $\approx \frac{2}{3} \sigma$
$\therefore 12 \approx \frac{2}{3} \sigma$
$ \therefore \sigma \approx \frac{12 \times 3}{2} \approx 18$
Hence, the value of standard deviation obtained is $18 .$

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