In the class intervals $10-20$ and $20-30$,the number $20$ is included in:

The class mark of a frequency distribution with equal sizes of two successive classes is $72$ and $77$. Then,the width of the class is ...........

The mean of $3, -3, -3, 3, 3, -3$ is ..........

If $\bar{x}$ is the mean of $x_{1}, x_{2}, \ldots, x_{n}$ and $\bar{y}$ is the mean of $y_{1}, y_{2}, \ldots, y_{n}$. If $\bar{z}$ is the mean of $x_{1}, x_{2}, \ldots, x_{n}, y_{1}, y_{2}, \ldots, y_{n}$,then $\bar{z}$ is equal to

Find the mean,the median,and the mode of the observations:
$33, 92, 55, 90, 35, 77, 58, 41, 80, 64, 46$

If $\bar{x}_{1}, \bar{x}_{2}, \bar{x}_{3}, \ldots, \bar{x}_{n}$ are the means of $n$ groups with $n_{1}, n_{2}, \ldots, n_{n}$ number of observations respectively,then the combined mean $\bar{x}$ of all the groups taken together is given by: