This question's explanation and your answers so far.
一般的なウォータフォールモデルで開発を行うプロジェクトにおいて，プロジェクトの経過とともに必要となる要員の数と，変更や間違いが発生したときに訂正作業に掛かる1件当たりのコストについて図にしたもののうち，適切な組合せはどれか。ここで，各グラフは縦軸が「大／小」，横軸が「プロジェクトの経過時間」を表す。 - 図a：プロジェクトの中盤から後半にかけてピークに達し，その後減少する山型の曲線。 - 図b：時間の経過とともに右肩上がりに急増していく曲線。 - 図c：開始時が大きく，時間の経過とともに右肩下がりに減少していく曲線。 - 図d：時間が経過してもほぼ一定（水平）の線。
正解 The correct answer is ア (number of staff = Graph a / correction cost = Graph b). In the waterfall model, the phases proceed in one direction from upstream to downstream. The number of staff required is small in the early requirements-definition and design phases, reaches its maximum in the middle-to-late phase when implementation (programming) is in full swing, and then decreases as the project moves into testing and migration. This pattern of “starting small, peaking in the middle-to-late phase, and then declining” matches the mountain-shaped Graph a. On the other hand, the cost of correcting a change or mistake grows as its impact spreads and rework increases the further downstream it is discovered, so the cost per case rises sharply as time passes. This steeply rising pattern matches Graph b. Therefore ア, the combination of staff = a and cost = b, is appropriate.
Assigning Graph a (mountain-shaped) to the number of staff is correct, but assigning Graph c (starts high and decreases downward) to the correction cost is wrong. Because rework grows and costs rise the further downstream the phase, the correction cost has an increasing trend (Graph b); Graph c, which decreases over time, is the opposite of reality.
It assigns Graph b (rising steeply) to the number of staff, but the staff count is a mountain shape (Graph a) that peaks during implementation and declines toward the end—it does not keep increasing to the very end. Assigning Graph d (roughly constant) to the correction cost also fails to match the reality that costs rise the further downstream (Graph b), so it is wrong.
It assigns Graph d (roughly constant) to the number of staff, but in reality the staff count rises and falls by phase and peaks during implementation—a mountain shape (Graph a), not constant. Assigning Graph c (downward) to the correction cost is also the opposite of the reality that costs rise the further downstream (Graph b), so it is wrong.