問94
頻出度★★★
ある機械の組立て作業のメンバになった P さんは，リーダの指導の下，作業工程を確認するためにアローダイアグラムを作成した。作成したアローダイアグラムは，効率よく作業を進行させるために，メンバ間で共有することにした。図 1 にアローダイアグラムを示す。 各工程は 1 人で行うものとして計画し，メンバの誰が担当しても予定日数で作業を終了するものとする。 図1の各工程を予定日数どおりに終了する場合, この組立て作業は何日で完了するか。
平成27年度 秋期 ITパスポート試験 問94
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 94
※ Our check while writing this explanation could not fully confirm the published answer; scoring follows IPA's official key.
Incorrectア
10 days is merely the required days of one relatively short path in Figure 1. The completion time is decided by the critical path (the longest path), not the shortest path, so at day 10 the processes on the longer parallel paths have not yet finished, and the whole work cannot be considered complete.
Incorrectイ
12 days is likewise the sum of a path shorter than the longest path. Looking only at the side with fewer days among the parallel paths underestimates the completion time. Completing all processes requires the 16 days of the longest path, so 12 days is not enough.
Incorrectウ
14 days is close to 16 days, but it is the error that arises when part of the critical path is missed in the count. Following the longest path correctly gives 16 days, so at 14 days all processes are not yet complete.
- エ
正解 In an arrow diagram (PERT chart), if every process advances exactly on its scheduled number of days, the completion time of the whole assembly work equals the number of days of the longest path from the start point to the end point — that is, the critical path. In Figure 1 several paths run in parallel; comparing the required days of each path and following the longest one gives a total of 16 days. Every other path is 16 days or fewer, and all processes finish only after the longest path ends at day 16, so the completion time is 16 days and the correct answer is エ.
ここがポイント
- In an arrow diagram (PERT chart), the days needed to finish all processes on schedule equal the number of days of the longest path from start to end — that is, the critical path.
- The completion time is always decided by the longest path, not by the shortest path or an average, so when parallel paths exist, compare the required days of all paths and take the maximum.
用語