To find the average income, we use the formula:
\[\text{Average Income} = \frac{\text{Total Income}}{\text{Number of Members}}\]
Substituting the values:
\[\text{Total Income} = 50,000 + 40,000 + 20,000 + 20,000 = 1,30,000\]
\[\text{Number of Members} = 4\]
\[\text{Average Income} = \frac{1,30,000}{4} = 32,500\]
The average monthly income of the family is Rs. 32,500/-.