Look at the table given below:

Marks	0-10	11-20	21-30	31-40
No. Of students	6	9	11	4

The true lower limit of the class 21-30 is

The given class interval is in the form of inclusive form.

To find out the true lower limit of the class we need to draw the table in continuous frequency distribution in exclusive form.

So, as we can see that true lower limit of class 21 – 30 is 20.5