Which formula is used to calculate the weighted mean?

The following data gives the distribution of height of students. The median of the distribution is:

Height (in $cm$)	$160$	$150$	$152$	$161$	$156$	$154$	$155$
No of students	$12$	$8$	$4$	$4$	$3$	$3$	$7$

If four different subjects are assigned weights in an examination as Physics $(2)$,Chemistry $(1)$,English $(1)$,and Mathematics $(2)$,and a student scores $60$ in Physics,$70$ in Chemistry,$70$ in English,and $80$ in Mathematics,find the weighted mean.

The mean of a set of $n$ numbers,when each is divided by $5$,is $\frac{X}{5}$. What is the mean of the original $n$ numbers?

Let $x_1, x_2, \ldots, x_{11}$ be $11$ distinct positive integers. If we replace the largest of these integers by the median of the other $10$ integers,then:

If the values $1, \frac{1}{2}, \frac{1}{3}, \frac{1}{4}, \frac{1}{5}, \dots, \frac{1}{n}$ occur at frequencies $1, 2, 3, 4, 5, \dots, n$ in a distribution,then the mean is