What is the average period for calculating the interest on drawing if a partner withdraws drawings of an equal amount in the middle of every quarter?

6 months

The correct answer is option 4- 6 months.

Average period = (Time left after 1st drawing + Time left after last drawing) / 2
                       = (10.5 + 1.5)/2
                       = 12/2
                       = 6 months