Frequency of Class Interval 20-30 in a 'Less than' Cumulative Frequency Table


A 'less than' cumulative frequency table is a type of frequency table that shows the cumulative frequency of observations that are less than or equal to a particular value or class interval.


Let's take an example of a 'less than' cumulative frequency table:

| Class Interval | Frequency | Cumulative Frequency |
|----------------|-----------|----------------------|
| 0-10 | 5 | 5 |
| 10-20 | 8 | 13 |
| 20-30 | ? | 25 |
| 30-40 | 10 | 35 |
| 40-50 | 7 | 42 |


To find the frequency of a class interval in a 'less than' cumulative frequency table, we need to subtract the cumulative frequency of the previous class interval from the cumulative frequency of the desired class interval.

Formula: Frequency of a Class Interval = Cumulative Frequency of the Desired Class Interval - Cumulative Frequency of the Previous Class Interval


Using the formula mentioned above, we can calculate the frequency of the class interval 20-30 in the given example:

Frequency of Class Interval 20-30 = Cumulative Frequency of Class Interval 20-30 - Cumulative Frequency of Class Interval 10-20

Frequency of Class Interval 20-30 = 25 - 13

Frequency of Class Interval 20-30 = 12

Therefore, the frequency of the class interval 20-30 is 12.


The 'less than' cumulative frequency table given above shows that the cumulative frequency of the class interval 10-20 is 13 and the cumulative frequency of the class interval 20-30 is 25. This means that there are 13 observations that are less than or equal to 20 and 25 observations that are less than or equal to 30. Therefore, the frequency of the class interval 20-30 can be found by subtracting the cumulative frequency of the previous class interval (10-20) from the cumulative frequency of the desired class interval (20-30). The resulting value (12) represents the number of observations that fall in the class interval 20-30.