位置4的问题 (Activity T) Suppose activity T has an earliest start time (EST) of 8, an earliest finish time (EFT) of 13, a latest start time (LST) of 12, and a latest finish time (LFT) of 17. Then, the activity can be STARTED anytime between ___ and ___.8, 128, 1312, 1312, 17单项选择题
A
8, 12
B
8, 13
C
12, 13
D
12, 17

Question

位置4的问题 (Activity T) Suppose activity T has an earliest start time (EST) of 8, an earliest finish time (EFT) of 13, a latest start time (LST) of 12, and a latest finish time (LFT) of 17. Then, the activity can be STARTED anytime between _ and _.8, 128, 1312, 1312, 17单项选择题

A

8, 12

B

8, 13

C

12, 13

D

12, 17

BlackTom AI · Accepted Answer

EST is 8 and LST is 12, so the activity’s allowable start window is between those two start times.

1) Relevant knowledge points and concepts
- EST (Earliest Start Time): the earliest time the activity can begin (given predecessors).
- EFT (Earliest Finish Time): EFT = EST + duration.
- LST (Latest Start Time): the latest time the activity can begin without delaying the project.
- LFT (Latest Finish Time): LFT = LST + duration.
- Slack (total float) = LST − EST, the amount the start can be delayed.

2) Step-by-step reasoning
- The question asks when the activity can be STARTED; therefore we compare start times (EST and LST), not finish times.
- The earliest possible start is EST = 8.
- The latest permissible start is LST = 12.

3) Calculations and intermediate steps
- Duration = EFT − EST = 13 − 8 = 5 time units.
- Check consistency: LFT should equal LST + duration = 12 + 5 = 17, which matches the given LFT = 17.
- Slack = LST − EST = 12 − 8 = 4; the activity can be delayed up to 4 units and still not affect the project finish.

4) Why the correct answer is correct
- Because start decisions use start times, the allowable start interval runs from the earliest start (8) to the latest start (12). Any start before 8 violates predecessor constraints; any start after 12 would push the project beyond its allowed schedule.

5) Why other options are incorrect
- "8, 13": mixes EST with EFT (a finish time), not the latest start; 13 is a finish time, not the latest start.
- "12, 13": mixes LST (a start time) with EFT (a finish time); the second value should be a latest start, not a finish time.
- "12, 17": combines LST (a start time) and LFT (a finish time); the question asks for the start interval, so both bounds should be start times.