If the mean of the set of numbers ${x_1}, {x_2}, {x_3}, ..., {x_n}$ is $\bar x$,then the mean of the numbers ${x_i} + 2i$,$1 \le i \le n$ is

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.

If for some positive $x \in R$,the frequency distribution of the marks obtained by $20$ students in a certain test is as follows:

Marks	$2$	$3$	$5$	$7$
Frequency	$(x+1)^2$	$2x-5$	$x^2-3x$	$x$

Then the mean of the marks is:

$A$ student scores $75\%, 80\%,$ and $85\%$ in three subjects. If the marks of a fourth subject are added,what is the minimum possible average percentage?

If the values $1, \frac{1}{2}, \frac{1}{3}, \dots, \frac{1}{n}$ have frequencies $1, 2, 3, \dots, n$ respectively,what is their mean?

What is the median of an ordered series of $n$ even observations?