For a given frequency distribution,$A=49.5, \Sigma f_{i}=40, \Sigma f_{i} u_{i}=-5$ and $c=20$. Then,mean $\bar{x}=$ ............

For a given frequency distribution,the total frequency is $25$ and $\Sigma f_{i} x_{i} = 120$. Then,the mean is $\ldots$

The mean of the following frequency distribution is $18$. Find the missing frequency $f$.

Class	$11-13$	$13-15$	$15-17$	$17-19$	$19-21$	$21-23$	$23-25$
Frequency	$3$	$6$	$9$	$13$	$f$	$5$	$4$

If $x_{i}$ are the midpoints of the class intervals of grouped data,$f_{i}$ are the corresponding frequencies,and $\bar{x}$ is the mean,then $\sum (f_{i} x_{i} - f_{i} \bar{x})$ is equal to

In a maths test taken by $40$ students,the average score of $30$ boys is $16$ and the average score of $10$ girls is $12$. Which of the following gives the average score of the whole class?

In the formula $\bar{x} = \frac{\Sigma f_{i} x_{i}}{\Sigma f_{i}}$,$\Sigma f_{i}$ represents ........