ANS:D - 20

To calculate the percentage discharge passing through non-monsoon periods, we first need to determine the proportion of sewage and drainage during non-monsoon periods. Given:

• Ratio of drainage to sewage = 20

This means that for every 20 units of drainage, there is 1 unit of sewage. Now, during non-monsoon periods, both drainage and sewage are likely to be present, but the proportion of sewage may be lower than during monsoon periods. If we assume that the proportion of sewage to drainage remains the same during non-monsoon periods, then the percentage discharge passing through non-monsoon periods can be calculated as: Percentage discharge passing through non-monsoon periods=11+20×100%Percentage discharge passing through non-monsoon periods=1/ 1+20​×100% =1 /21×100% ≈4.76% Therefore, the percentage discharge passing through non-monsoon periods is approximately 5%.