What is the standard deviation of the followi | vedclass

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(C) To find the standard deviation,we first calculate the midpoints $(x_i)$ and use the assumed mean method.      Class $(x_i)$    $f_i$    $d_i = x_i

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$9$

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(C) To find the standard deviation,we first calculate the midpoints $(x_i)$ and use the assumed mean method.      Class $(x_i)$    $f_i$    $d_i = x_i - 25$    $f_i d_i$    $f_i d_i^2$        $0-10$ $(5)$    $1$    $-20$    $-20$    $400$        $10-20$ $(15)$    $3$    $-10$    $-30$    $300$        $20-30$ $(25)$    $4$    $0$    $0$    $0$        $30-40$ $(35)$    $2$    $10$    $20$    $200$        Total    $N = 10$    -    $\sum f_i d_i = -30$    $\sum f_i d_i^2 = 900$  The variance is given by:$\sigma^2 = \frac{\sum f_i d_i^2}{N} - \left( \frac{\sum f_i d_i}{N} \right)^2$$\sigma^2 = \frac{900}{10} - \left( \frac{-30}{10} \right)^2$$\sigma^2 = 90 - (-3)^2 = 90 - 9 = 81$Therefore,the standard deviation $\sigma = \sqrt{81} = 9$.

What is the standard deviation of the following series?

Class $0-10$ $10-20$ $20-30$ $30-40$

Freq $1$ $3$ $4$ $2$

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What is the standard deviation of the following series? Class $0-10$ $10-20$ $20-30$ $30-40$ Freq $1$ $3$ $4$ $2$