When the investigator has personally obtained the information for a particular purpose,this data is called ........ data.

If the marks obtained by the $20$ students are $6, 4, 9, 5, 9, 3, 7, 7, 5, 6, 9, 4, 10, 10, 4, 3, 6, 7, 9, 9$,then the mode of this data is .............

The following table gives the frequencies of most commonly used letters $a, e, i, o, r, t, u$ from a page of a book:

Letters	$a$	$e$	$i$	$o$	$r$	$t$	$u$
Frequency	$75$	$125$	$80$	$70$	$80$	$95$	$75$

Represent the information above by a bar graph.

Obtain the mean of the following distribution:

Frequency $(f_i)$	Variable $(x_i)$
$4$	$4$
$8$	$6$
$14$	$8$
$11$	$10$
$3$	$12$

The marks obtained (out of $50$ marks) by $30$ students in a mathematics test are as given below:
$37, 22, 35, 42, 10, 16, 31, 22, 20, 27$
$27, 20, 31, 40, 35, 40, 27, 16, 47, 22$
$40, 22, 35, 20, 37, 20, 37, 47, 42, 31$
Represent this data in a frequency distribution table.

If the mean of the observations $x, x+3, x+5, x+7, x+10$ is $9,$ find the mean of the last three observations.