Calculate the arithmetic mean from the following given data using assumed mean method:

$x_i$	$10$	$20$	$30$	$40$
$f_i$	$2$	$3$	$4$	$1$

The mean of a data set comprising of $\mathrm{16}$ observations is $\mathrm{16}$. If one of the observation value $\mathrm{16}$ is deleted and three new observations valued $3,\; 4$ and $\mathrm{5}$ are added to the data, then the mean of the resultant data is

If for some $x\in R$, the frequency distribution of the marks obtained by $20$ students in a test is:

Then the mean of the marks is :