Final answer:
The average seek time is approximately 5 milliseconds.
Step-by-step explanation:
The average seek time can be calculated by taking the sum of the time it takes for each type of seek, divided by the number of seeks. In this case, there are two types of seeks: seek to an adjacent cylinder and a full-stroke seek over all 5,000 cylinders.
Let's assume that the full-stroke seek happens once every 5,000 seeks. Therefore, the average seek time would be:
((1 millisecond * 4,999 seeks) + (18 milliseconds * 1 seek)) / 5,000 total seeks = 4.9992 milliseconds ≈ 5 milliseconds.