What is the value of $x$ if the mean of $8, 6, 7, 5, x,$ and $4$ is $7$?

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 relation between the median $M$,the second quartile ${Q_2}$,the fifth decile ${D_5}$,and the $50^{th}$ percentile ${P_{50}}$ of a set of observations 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 ${d_i}$ is the deviation of a class mark ${y_i}$ from $a$,the assumed mean,and ${f_i}$ is the frequency,if ${M_g} = x + \frac{1}{{\sum {f_i}}}(\sum {f_i}{d_i})$,then $x$ is:

Find the mean of the following frequency distribution:

$x_i$	$5$	$15$	$25$	$35$	$45$	$55$
$f_i$	$12$	$18$	$27$	$20$	$17$	$6$