Explanation:

The time which results in the least possible direct cost of an activity is called the optimum time. It is also known as the most efficient time to complete an activity. To calculate the optimum time, we need to consider three different times: normal time, crash time, and slow time.

Normal Time:
Normal time is the time needed to complete an activity under normal working conditions. This time is estimated based on the average performance of the workers and the availability of resources. It is the time taken to complete an activity without any additional resources or working hours.

Crash Time:
Crash time is the shortest possible time to complete an activity by using additional resources or working hours. This time is achieved by increasing the workforce, using more efficient equipment, or working overtime. The crash time is always shorter than the normal time.

Slow Time:
Slow time is the longest possible time to complete an activity by using fewer resources or working hours. This time is achieved by decreasing the workforce, using less efficient equipment, or working fewer hours. The slow time is always longer than the normal time.

Optimum Time:
The optimum time is the time that results in the least possible direct cost of an activity. It is the most efficient time to complete an activity, which balances the cost and the time required to complete the activity. The optimum time is calculated by considering the normal time, crash time, and slow time, and selecting the time that provides the best balance between cost and time.

In conclusion, the optimum time is the time that results in the least possible direct cost of an activity. It is achieved by balancing the cost and the time required to complete an activity. The optimum time is calculated by considering the normal time, crash time, and slow time, and selecting the time that provides the best balance between cost and time.