The mean weight per student in a group of seven students is $55 \ kg$. If the individual weights of $6$ students are $52, 58, 55, 53, 56$ and $54 \ kg$,then the weight of the seventh student is.....$kg$.

The mean marks of $100$ students in a class in mathematics is $72$. If the number of boys is $70$ and their mean marks is $75$,find the mean marks of the girls in the class.

Find the median of the numbers $6, 14, 12, 8, 10, 9, 11$.

If in an examination different weights are assigned to different subjects: Physics $(2)$,Chemistry $(1)$,English $(1)$,and Mathematics $(2)$. If a student scored $60$ in Physics,$70$ in Chemistry,$70$ in English,and $80$ in Mathematics,then his weighted $A.M.$ is:

If the mean of the numbers $27, 31, 89, 107, 156$ is $82$,what is the mean of the numbers $130, 126, 68, 50, 1$?

If the mean of the series $x_1, x_2, ......., x_n$ is $\bar{x}$,then what will be the mean of the series $x_i + 2i, (i = 1, 2, ......., n)$?