If the path A-B-F-J has a total duration of 12 days, what is the duration of F?

• A. 5 days
• B. 6 days
• C. 7 days
• D. 8 days

Answer: (C)

Think of the path duration as the sum of the durations of each segment along that route. A-B-F-J consists of three segments: A-B, B-F, and F-J. The total time along this path is fixed, so the time spent on the middle segment (the one that corresponds to F) is whatever remains after you subtract the durations of the other two segments from the total.

From the diagram, A-B lasts four days and F-J lasts one day. Subtracting those from the total twelve days leaves seven days for the middle segment. So the duration associated with F is seven days. Check: four plus seven plus one equals twelve, which matches the total. If the surrounding durations were different, you’d simply subtract them from the total to find the duration of F.