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

Find the mean of the following frequency distribution:

$x_i$	$3$	$6$	$9$	$12$
$f_i$	$1$	$2$	$3$	$4$

If the arithmetic mean of the numbers $x_1, x_2, x_3, ..., x_n$ is $\bar{x}$,then the arithmetic mean of the numbers $ax_1 + b, ax_2 + b, ax_3 + b, ..., ax_n + b$,where $a$ and $b$ are two constants,would be:

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 upper quartile for the following distribution is given by the size of:

Size of Item	$1$	$2$	$3$	$4$	$5$	$6$	$7$
Frequency	$2$	$4$	$5$	$8$	$7$	$3$	$2$

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