問43
頻出度★★★
図のアローダイアグラムにおいて，作業 B が2日遅れて完了した。そこで，予定どおりの期間で全ての作業を完了させるために，作業 D に要員を追加することにした。作業 D に当初20名が割り当てられているとき，作業 D に追加する要員は最少で何名必要か。ここで，要員の作業効率は一律である。
令和4年度 ITパスポート試験 問43
マネジメント系プロジェクトマネジメント › プロジェクトマネジメント
This question's explanation and your answers so far.
解説
問 43
Incorrectア
2 comes from mistaking the 2 days of delay directly for the number of people to add. Adding only 2 people (22 in total) takes 200 person-days ÷ 22 people ≈ 9.1 days, so starting from day 12 at the node runs past day 21 and misses the scheduled 20 days.
Incorrectイ
With 3, adding 3 people (23 in total) gives 200 person-days ÷ 23 people ≈ 8.7 days, which does not fit within the required 8 days. 12+8.7 ≈ 20.7 days still exceeds the scheduled 20 days.
Incorrectウ
With 4 as well, adding 4 people (24 in total) gives 200 person-days ÷ 24 people ≈ 8.3 days, which slightly exceeds 8 days and so does not make it in time. Exactly 8 days requires 25 people (5 added); with 24 people it falls short by about 0.3 days.
- エ
正解 The correct answer is エ (5 people). First, find the critical path: A→C→D = 5+5+10 = 20 days and B→D = 10+10 = 20 days are the longest, so the scheduled duration is 20 days. The node where tasks C and B merge (the start point of task D) is normally reached on day 10 (10 days via A→C, and 10 days via B). If task B now finishes 2 days late, arrival at this node slips to day 12. Among the paths from this node to the end point, E→F takes 12+4+4 = 20 days and stays within schedule, but task D, starting on day 12 and taking 10 days, would end on day 22, exceeding the schedule by 2 days. To finish within the planned 20 days, task D must be shortened to within 20−12 = 8 days. Since work efficiency is uniform, the total workload of task D stays constant at the initial 20 people × 10 days = 200 person-days. Finishing this in 8 days requires 200÷8 = 25 people, which is 25−20 = 5 more than the initial 20. Therefore, the minimum number to add is 5.
ここがポイント
- In an arrow diagram, find the critical path (the longest path = the scheduled duration) and the earliest arrival time at each node, then judge how a task's delay affects the final project duration.
- When work efficiency is uniform, the total workload (person-days) is fixed, and required days = total person-days ÷ number of people. To shorten task D from 10 days to 8 days requires 200 person-days ÷ 8 days = 25 people, so add the 5-person difference from the initial 20.
用語