When a partner draws a fixed amount at the end of every quarter, the interest on drawings is calculated for an average period depending on the timing of the drawings. For quarterly drawings made at the **end of each quarter**, the average period is calculated as follows:
Step 1: Calculating the average period:
For quarterly drawings at the end of each quarter:
\[
\text{Average period} = \frac{3 + 6 + 9 + 12}{4} = 7.5 \ \text{months}.
\]
However, based on the **stated interest amount** (\rupee 9,000), the actual average period used was \(4 \frac{1}{2}\) months. This suggests an error in standard assumptions or specific adjustments in the calculations.
Step 2: Verifying the correct average period:
If the interest on drawings for the year matches \rupee 9,000, and the fixed rate of interest is \(15\% \text{ p.a.}\), this aligns with an **average period** of \(4 \frac{1}{2}\) months.
Conclusion:
The interest on drawings was calculated using an average period of \(4 \frac{1}{2}\) months.