Question

The blood group of $30$ students of class ${\text{VIII}}$ are as follows:

$A$	$B$	$O$	$O$	$AB$
$O$	$A$	$O$	$B$	$A$
$O$	$B$	$A$	$O$	$O$
$A$	$AB$	$O$	$A$	$A$
$O$	$O$	$AB$	$B$	$A$
$O$	$B$	$A$	$B$	$O$

Find the most common and rare blood group?

Answer 1

Hint: Make the frequency table of all the blood groups by calculating the number of blood groups of each type and then check the most rare and most common blood group.

Complete step-by-step answer:
In statistics the frequency of an event is the number of times the observation occurred/recorded in an experiment or study. These frequencies are often graphically represented in histograms.
Make the frequency table for the blood group of students by calculating the number of students of each blood group:

Blood Group	Number of students
$A$	$9$
$B$	$6$
$AB$	$3$
$O$	$12$

As most of the students have a blood group $O$ and a very less number of students have $AB$ blood group.
Therefore, $AB$ is rare and $O$ is the most common blood group.
So, the correct answer is “, $AB$ is rare and $O$ is the most common blood group.”.

Note: Count the number of students having the same type of blood group for each type very patiently to avoid any confusion and make a frequency table of it. Since there are a total of 30 students the sum of the frequency must match the total number of students.