If $Z - M = 4$,then $M - \bar{x} = \dots$

The median class in the following frequency distribution is ..........

Class	$20-25$	$25-30$	$30-35$	$35-40$	$40-45$	$45-50$	$50-55$
Frequency	$2$	$5$	$8$	$10$	$7$	$10$	$3$

Find the mean of the following frequency distribution:

Class	$21-25$	$26-30$	$31-35$	$36-40$	$41-45$	$46-50$	$51-55$
Frequency	$18$	$32$	$30$	$40$	$25$	$15$	$40$

(in $.675$)

In a frequency distribution with total frequency $48$,$\bar{x}=70$,$\Sigma f_{i}=43+f$,and $A=66$. Then,the missing frequency $f=$ .........

The mean of $15$ observations is $16$. If $2$ is added to each observation and then each result is divided by $3$,the new mean is:

In the formula $M = l + \frac{(\frac{n}{2} - cf)}{f} \times h$ for the median,$h = \ldots \ldots \ldots$