The blood groups of $30$ students of Class VIII are recorded as follows:
$A, B, O, O, AB, O, A, O, B, A, O, B, A, O, O, A, AB, O, A, A, O, O, AB, B, A, O, B, A, B, O$
Represent this data in the form of a frequency distribution table. Which is the most common, and which is the rarest, blood group among these students?

Given:

The blood groups of $30$ students of class VIII are recorded as follows:

$A, B, O, O, AB, O, A, O, B, A, O, B, A, O, O, A, AB, O, A, A, O, O, AB, B, A, O, B, A, B, O$.

To do:

We have to represent this data in the form of a frequency distribution table and out which is the most common and which is the rarest blood group among these students.

Solution:

The required frequency distribution is: 

Blood group	Tally marks	Number of students
A	|||| ||||	9
B	|||| |	6
AB	|||	3
O	|||| |||| ||	12
Total		30

 The most common blood group is the blood group with highest frequency $O$ and the rarest blood group is the blood group with lowest frequency $AB$.