Find the median of the observations $18, 8, 12, 3, 20, 4, 10, 5$.

The lengths of $62$ leaves of a plant are measured in millimetres and the data is represented in the following table:

Length (in mm)	Number of leaves
$118-126$	$8$
$127-135$	$10$
$136-144$	$12$
$145-153$	$17$
$154-162$	$7$
$163-171$	$5$
$172-180$	$3$

Draw a histogram to represent the data above.

The blood groups of $30$ students are recorded as follows:
$A, B, O, A, AB, O, A, O, B, A, O, B, A, AB, B, A, AB, B$
$A, A, O, A, AB, B, A, O, B, A, B, A$
Prepare a frequency distribution table for the data.

The mean of the following distribution is $50$. Find the value of $a$ and hence the frequencies of $30$ and $70$.

$x$	$f$
$10$	$17$
$30$	$5a+3$
$50$	$32$
$70$	$7a-11$
$90$	$19$

For drawing a frequency polygon of a continuous frequency distribution,we plot the points whose ordinates are the frequencies of the respective classes and abscissae are respectively:

The frequency distribution of the marks scored by $35$ students in a $60$ marks test is as below:

Marks scored	No. of students
$0-10$	$2$
$10-20$	$7$
$20-30$	$8$
$30-40$	$7$
$40-50$	$8$
$50-60$	$3$

Represent the data by a histogram.