問48
頻出度★★★
システム開発プロジェクトにおいて，同じ規模のプログラムを36本作成する計画がある。1週間当たり6本のプログラムを作成できるA氏だけに依頼する予定であったが，計画変更によって，A氏と，A氏の半分の生産性のB氏の2名に依頼することにした。A氏とB氏の1週間当たりの費用がそれぞれ30万円と20万円であるとき，当初の計画に比べた費用の変更は幾らか。ここで，A氏とB氏は作業を並行して実施し，A氏とB氏の作業効率は常に一定であるものとする。
平成30年度 秋期 ITパスポート試験 問48
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 48
Incorrectア
“A decrease of 800,000 yen”. In reality it is an increase of 200,000 yen, so the direction of decrease itself is wrong. Adding Mr. B shortens the work period, but the weekly cost rises, so the total does not decrease. This option shows the largest saving and is a wrong answer that overestimates only the effect of shortening the period.
Incorrectイ
“A decrease of 300,000 yen”. If you mistakenly assume Mr. B's productivity is the same as Mr. A's at 6 programs per week, the total becomes 12 programs per week over 3 weeks, with a cost of 3 weeks × 500,000 yen ＝ 1,500,000 yen, which would be calculated as a decrease of 300,000 yen from 1,800,000 yen. However, Mr. B is half of Mr. A (3 programs per week), so the correct figure is a total of 9 programs per week over 4 weeks, and this value does not hold.
- ウ
正解 First, find the cost of the original plan. Mr. A can create 6 programs per week, so creating 36 takes 36÷6＝6 weeks, and the cost is 6 weeks × 300,000 yen ＝ 1,800,000 yen. Next, find the cost after the change. Mr. B's productivity is half that of Mr. A, i.e., 3 programs per week, and since the two work in parallel, the total is 6＋3＝9 programs per week. Creating 36 takes 36÷9＝4 weeks, and the cost is 4 weeks × (300,000 yen ＋ 200,000 yen) ＝ 4 weeks × 500,000 yen ＝ 2,000,000 yen. Therefore, after the change it increases by 2,000,000 yen － 1,800,000 yen ＝ 200,000 yen compared with the original, so the correct answer is “ウ”. The key point is that adding Mr. B shortens the period from 6 weeks to 4 weeks, but the weekly payment increases from 300,000 yen to 500,000 yen, so the total actually increases by 200,000 yen.
Incorrectエ
“An increase of 1,200,000 yen”. This wrong answer assumes the work period stays at 6 weeks even after adding Mr. B, calculating 6 weeks × 500,000 yen ＝ 3,000,000 yen and treating the 1,200,000 yen difference from 1,800,000 yen as the increase. In reality the total is 9 programs per week and the period is shortened to 4 weeks, so it fails to reflect the shortened period and is an overestimate.
ここがポイント
- A basic calculation of productivity, effort, and cost: find the required number of weeks by work volume (36 programs) ÷ productivity (programs per week), then compute the total cost as weeks × weekly cost.
- Adding staff can shorten the work period, but since the weekly cost increases, the total does not necessarily go down. The idea is to compare by total cost, multiplying both the period and the unit price.
用語