When equal amounts are withdrawn at the beginning of every month throughout the year, the interest on partner's drawings are charged for how many months on average method basis?

6.5

The correct answer is option 3- 6.5.

When the amount is withdrawn at the first day of each month
Ist drawing = 1 April so months left after it was 12 months
Last drawing = 1 March so months left after it was 1 month
Average Period = (No. of months left after 1 drawings + No. of months left after last drawings)/2
                      = (12+1)/ 2
                      = 6.5 months

Average period is calculated for calculating interest on drawings and the average period depends on the timing of withdrawal.
The formula for calculating the average period is = (Months left after Ist drawing + Months left after last drawing) / 2
After calculating the average period interest on drawings is calculated. The formula for calculating interest on drawing is = Total drawings X (Rate of interest/100) X (Average period/12).