Class frequency refers to the number of data values that lie in a given class interval. Let us try to understand this by looking at an example.
Example of Class Frequency:
Suppose that we are given the data about marks obtained by 25 students in an exam as follows,
Now, let us find the class frequency of each of the given class intervals.
- The frequency of the class interval 60-65 is 7. This means that 7 students obtained a percentage between 60 to 65 percent.
- The frequency of the class interval 65-70 is 5. This means that 5 students obtained a percentage between 65 to 70 percent.
- The frequency of the class interval 70-75 is 6.
- The frequency of the class interval 75-80 is 4.
- The frequency of the class interval 80-85 is 3.
A single bunch of tally marks consisting of 4 vertical lines and a line crossing them represents a frequency of 5.
For example, in the class interval 60-65 we have 5 + 2 = 7, students. This is because we have a bunch of five tally marks and 2 vertical lines for that class interval. This tells us there 7 students lying in that class interval.
How to find the Class Frequency?
- In order to find the class frequency, we must first make sure that the data is divided into class intervals of equal length.
- Then for each class interval, we count the number of data values lying in that class.
- Then the class frequency is nothing but the number of data values lying in that class.
Example 2:
Suppose that we are given the following set of data values,
What is the frequency of the class interval 20-25?
To find the class frequency we simply count the number of data values lying between 20 and 25.
The values 25 and 20 occur in the first row. (TWO Observations)
The value 22 occurs in the eight row. (ONE Observation)
The value 25 occurs in the ninth row. (ONE Observation)
So, the frequency of class interval 20-25 is equal to,
Class Frequency of 20-25 = 2 + 1 + 1 = 4
We can similarly find the class frequency of the other class intervals.
Related Articles:
Class Width – Explained with Examples
What is the Class Width for a Histogram? (with Examples)
