問39
頻出度★★★
20本のプログラムを作成するに当たり，プログラム1本につき，作業期間が1日，コストが4万円と見積もり，作成に着手した。開始からの10日間で8本作成し，累積コストは36万円になっていた。残りのプログラムは未着手である。このままの生産性で進めると，見積りに対する超過コストは最終的に何万円になるか。
平成28年度 秋期 ITパスポート試験 問39
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 39
Incorrectア
40,000 yen only looks at the overrun already incurred on the 8 completed programs (8 × 5,000 yen = 40,000 yen, i.e., actual 360,000 yen − estimated 320,000 yen). But the question asks for the final cost overrun, and since it omits the additional overrun (60,000 yen) that will arise on the 12 not-yet-started programs, it falls short.
Incorrectイ
60,000 yen only counts the overrun that will arise on the remaining 12 not-yet-started programs (5,000 yen per program from 45,000 − 40,000, so 12 × 5,000 yen = 60,000 yen). Since it does not add the 40,000 yen overrun already incurred on the 8 completed programs, it falls short (40,000 yen + 60,000 yen = 100,000 yen is correct).
- ウ
正解 Each program is estimated at 40,000 yen, so the total estimate for 20 programs is 40,000 yen × 20 = 800,000 yen. From the actual results after starting (8 programs completed in 10 days with a cumulative cost of 360,000 yen), the actual cost per program is 360,000 yen ÷ 8 = 45,000 yen. Assuming this productivity (45,000 yen per program) continues unchanged, the final cost for all 20 programs is 45,000 yen × 20 = 900,000 yen. Therefore the cost overrun against the 800,000 yen estimate is 900,000 yen − 800,000 yen = 100,000 yen, so option ウ is correct. Broken down, the overrun per program is 45,000 − 40,000 = 5,000 yen; the overrun already incurred on the 8 completed programs is 8 × 5,000 yen = 40,000 yen, and the overrun that will arise on the remaining 12 not-yet-started programs is 12 × 5,000 yen = 60,000 yen, which together sum to 40,000 + 60,000 = 100,000 yen, matching the result above.
Incorrectエ
180,000 yen is a trap that leads to overestimating the overrun. For example, subtracting the 360,000 yen already paid from the actual cost of the remaining 12 programs, 12 × 45,000 yen = 540,000 yen (540,000 − 360,000 = 180,000), gives 180,000 yen by using the wrong baseline for the overrun. Correctly, the cost overrun = final cost of 900,000 yen (obtained by extrapolating the actual unit cost to all 20 programs) − total estimate of 800,000 yen = 100,000 yen, which is not 180,000 yen.
ここがポイント
- The idea of finding the actual cost per program (actual unit cost) by cumulative cost ÷ number completed, then extrapolating to the final cost of all the work (20 programs) on the premise that this unit cost continues.
- Cost overrun = extrapolated final cost − initial total estimate. You must add the overrun of both the already-incurred part (8 completed programs) and the not-yet-started part (remaining 12 programs); counting only one side gives the wrong answers ア=4 / イ=6. This is the CPI/EAC thinking of EVM.
用語