If $\mu$ is the mean of a distribution $(y_i, f_i)$,then $\sum f_i(y_i - \mu) = $

For a symmetrical distribution,if ${Q_1} = 25$ and ${Q_3} = 45$,the median is

$x_1, x_2, \dots, x_{34}$ are numbers such that $x_i = 150$ for all $i \in \{1, 2, \dots, 10\}$ and $x_{i+1} - x_i = -2$ for all $i \in \{10, 11, \dots, 33\}$. Find the median of $x_1, x_2, \dots, x_{34}$.

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.

For a distribution $x_1, x_2, \dots, x_{101}$ such that $x_1 < x_2 < x_3 < \dots < x_{100} < x_{101}$,the mean deviation of this distribution about a number $k$ is minimum. Then $k$ is equal to which of the following?

Which formula is used to calculate the weighted mean?