When probationary employees reach the end of their period, they will be placed in the overtime rotation equal to those employees with the average number of hours __________.

The correct choice indicates that probationary employees will be placed in the overtime rotation equal to those employees with the average number of hours plus 48. This means that their eligibility for overtime is not merely based on their hours worked but is instead aligned with those who have more experience and have consistently accumulated hours beyond a baseline of 48.

This approach reflects a system where overtime rotation prioritizes employees who have proven their commitment and consistency in work hours, which often comes with experience and time in the position. It ensures that probationary employees are integrated into the rotation in a manner that acknowledges the workload and dedication needed to fulfill the requirements of their roles effectively.

When looking at other choices, the reference points like under 40 or over 60 do not capture the standard or average base that many workplaces adopt. They either set the bar too low or too high, failing to reflect the realities of regular operational workloads in a firefighting environment. Hence, aligning probationary employees with those who have a workload that is a bit above 48 creates a fair and structured transition into the overtime rotation.