The frequency distribution:

$\begin{array}{|l|l|l|l|l|l|l|} \hline X & 2 & 3 & 4 & 5 & 6 & 7 \\ f & 4 & 9 & 16 & 14 & 11 & 6 \\ \hline \end{array}$

Find the standard deviation.

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$\begin{array}{|c|c|c|c|c|} \hline x_{i} & f_{i} & d_{i}=x_{i}-4 & f_{i} d_{i} & f_{i} d_{i}^{2} \\ \hline 2 & 4 & -2 & -8 & 16 \\ \hline 3 & 9 & -1 & -9 & 9 \\ \hline 4 & 16 & 0 & 0 & 0 \\ \hline 5 & 14 & 1 & 14 & 14 \\ \hline 6 & 11 & 2 & 22 & 44 \\ \hline 7 & 6 & 3 & 18 & 54 \\ \hline \text { Total } & n=60 & & \Sigma f_{i}=37 & \Sigma f_{i} d_{i}^{2}=137 \\ \hline \end{array}$

$ \therefore \quad SD =\sqrt{\frac{\Sigma f_{i} d_{i}^{2}}{n}-\left(\frac{\Sigma f_{i} d_{i}}{n}\right)^{2}}=\sqrt{\frac{137}{60}-\left(\frac{37}{60}\right)^{2}}=\sqrt{2.2833-(0.616)^{2}} $

$=\sqrt{2.2833-0.3794}=\sqrt{1.9037}=1.38 $

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What is the standard deviation of the following series

class $0-10$ $10-20$ $20-30$ $30-40$
Freq $1$ $3$ $4$ $2$

 

Let $x_1, x_2, x_3, x_4, .......... , x_n$ be $n$ observations and let $\bar x$ be their arithmetic mean and $\sigma ^2$ be their variance.

Statement $-1$ : Variance of observations $2x_1, 2x_2, 2x_3, ......, 2x_n$ is $4\sigma ^2$ .

Statement $-2$ : Arithmetic mean of $2x _1, 2x_2, 2x_3, ......, 2x_n$ is $4\bar x$ .

If $x_1, x_2,.....x_n$ are $n$ observations such that $\sum\limits_{i = 1}^n {x_i^2}  = 400$ and $\sum\limits_{i = 1}^n {{x_i}}  = 100$ , then possible value of $n$ among the following is