In the usual notations,$Z - M = \ldots \ldots \ldots \quad (M - \bar{x})$

Find the unknown entries $a, b, c, d, e, f$ in the following distribution of heights of students in a class:

Height (in $cm$)	Frequency	Cumulative frequency
$150-155$	$12$	$a$
$155-160$	$b$	$25$
$160-165$	$10$	$c$
$165-170$	$d$	$43$
$170-175$	$e$	$48$
$175-180$	$2$	$f$
Total	$50$	-

Find the mode of the following frequency distribution:

Class	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$	$80-90$
Frequency	$8$	$12$	$27$	$43$	$55$	$37$	$18$

The median class in the following frequency distribution is $\ldots \ldots \ldots \ldots .$

Class	$10-25$	$25-40$	$40-55$	$55-70$	$70-85$	$85-100$
Frequency	$5$	$21$	$21$	$8$	$25$	$20$

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

Consider the following frequency distribution of the heights of $60$ students of a class:

Height (in $cm$)	Number of students
$150-155$	$15$
$155-160$	$13$
$160-165$	$10$
$165-170$	$8$
$170-175$	$9$
$175-180$	$5$

The sum of the lower limit of the modal class and upper limit of the median class is: