Here, the maximum no. of students is 9, and the class corresponding to the frequency is 20 – 30.
So, the modal class is 20 – 30.
lower limit (l) of modal class = 20,
class size(h) = 10
frequency (f1) of the modal class = 9
frequency (f0) of class preceding the modal class = 5
frequency (f2) of class succeeding the modal class = 3
Now, let us substitute these values in the formula