The class length of the excluding type of class $20-30$ in a frequency distribution is .......

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 $Z = l + \left( \frac{f_{1} - f_{0}}{2f_{1} - f_{0} - f_{2}} \right) \times c$ for the mode,$f_{1} = \ldots \ldots \ldots$

Find the median of the following frequency distribution:

Class	$5-10$	$10-15$	$15-20$	$20-25$	$25-30$	$30-35$	$35-40$	$40-45$
Frequency	$5$	$6$	$15$	$10$	$5$	$4$	$2$	$2$

Cumulative frequency distribution is used to calculate the $\ldots \ldots \ldots$ of a frequency distribution.

For some given data,if $M + \bar{x} = 32$ and $M - \bar{x} = 2$,then $Z = \ldots \ldots \ldots$