Class Interval
2026-02-28 11:01 Diff
https://brightchamps.com/en-us/math/data/class-interval

To find class intervals of datasets accurately, we follow these steps:


Step 1: Find the range. 
To find the range of the dataset, subtract the minimum value from the maximum value. 
Range = maximum value - minimum value.


Step 2: Decide the number of intervals.
Choose how many class intervals you need, depending on the size of the data set and the level of details required. 


Step 3: Calculate the class width.
Determine the class width by dividing the range by the number of intervals selected.
Class width = range ÷ number of intervals.


Step 4: Set the class boundaries.
Start from the minimum value, then repeatedly add the class width to maintain the lower and upper limits of each interval. 


Step 5: Organize the data. 
Place each data point into its appropriate class interval based on the boundaries you have defined.

Let us practice through an example: 

A teacher records the ages of 12 students in a class as 10, 12, 14, 15, 13, 17, 18, 16, 19, 11, 13, 15. Organize the data using class intervals.

Solution: 

Step 1: First, we can find the range.
We know that the maximum value = 19, and the minimum value = 10. 
So, range \(= 19 - 10 = 9\).


Step 2: Since, we have 12 data points, we choose 4 intervals.


Step 3: Now, we can calculate the class width. 
We know that, class width = range ÷  number of intervals. 
Then class width \(= 9 ÷ 4 = 2.25\).
We can round it to the nearest whole number, 3. 


Step 4: We can set the class boundaries, starting from the minimum value 10, and by adding the class width 3. 
Hence, the classes will be: 

  • 10 -13
  • 13 -16
  • 16 -19
  • 19 -22

Here, we have added one extra interval to ensure that all values are covered. 


Step 5: Now we can organize the data into intervals. 

Class interval Data values Frequency 10 - 13 10, 12, 11, 13, 13 5 13- 16

14, 15, 15

3 16 - 19 16, 17, 18, 19 4 19 - 22  _ 0