Here, the maximum number of persons i.e. 30 have income in the interval 300 – 400.
So, the modal class is 300 – 400.
lower limit (l) of modal class = 300,
class size(h) = 100
frequency (f1) of the modal class = 30
frequency (f0) of class preceding the modal class = 18
frequency (f2) of class succeeding the modal class = 20
Now, let us substitute these values in the formula