When a partner withdraws a fixed amount at the end of every quarter, the average period for calculating interest is generally 7½ months. However, in this specific case, interest charged on Mishu's drawings amounted to ₹9,000, which reflects an average period of 4½ months instead of the usual average of 7½ months.
Step 1: Verify the given interest amount:
Interest on drawings formula: \[ \text{Interest} = \text{Total Drawings} \times \text{Rate of Interest} \times \frac{\text{Average Period}}{12}. \] Given that the total interest is ₹9,000 and the rate of interest is \(15\%\), the shorter average period of 4½ months can be confirmed based on the actual interest charged.
Conclusion:
Interest on Mishu's drawings was calculated for an average period of \(4½ \ \text{months}\).