Here, the maximum no. of students is 20, and the class corresponding to this 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 = 20
frequency (f0) of class preceding the modal class = 6
frequency (f2) of class succeeding the modal class = 10
Now, let us substitute these values in the formula