Since the maximum number of consumers (is 20) have got monthly consumption in the interval 120-140,

the model class is 120 -140.

The lower boundary (l) of the modal class = 120.

The class size (h) = 20

The frequency of modal class (f_{1}) = 20

The frequency of the class preceding the modal class (f_{0}) = 16.

The frequency of the class succeeding the modal class (f_{2}) = 14.

**Now, using the formula:**