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

The number of observations in a group is $40$. If the average of the first $10$ observations is $4.5$ and the average of the remaining $30$ observations is $3.5$,then the average of the whole group is:

Compute the median from the following table:

Marks obtained	No. of students
$0-10$	$2$
$10-20$	$18$
$20-30$	$30$
$30-40$	$45$
$40-50$	$35$
$50-60$	$20$
$60-70$	$6$
$70-80$	$3$

The mean of a set of numbers is $\bar{x}$. If each number is multiplied by $\lambda$,then the mean of the new set is

If the mean of the first $n$ natural numbers is equal to $\frac{n + 7}{3}$,then what is the value of $n$?

If the mean of five observations $x, x + 2, x + 4, x + 6$,and $x + 8$ is $11$,what is the mean of the last three observations?