Since the maximum families 40 lies in the class 1500 – 2000, this is the required modal class.

Lower boundary of the modal class (l) = 1500

Frequency of the modal class (f_{1}) = 40

Frequency of the class preceding the modal class f_{0} = 24

Frequency of the class succeeding the modal class f_{2} = 33

Height of the class, h = 500

Hence, modal monthly income = Rs. 1847.83.

Assumed mean (a) = 3250