問8
頻出度★☆☆
新規システムの構築を，新規開発又はパッケージ採用によって実施する場合の初期投資額，効果額，運用費，保守料が表のとおりであるとき，初期投資額の回収年数が最少となるものはどれか。
平成22年度 秋期 ITパスポート試験 問8
ストラテジ系システム企画 › システム化計画
This question's explanation and your answers so far.
解説
問 8
Incorrectア
Its net effect is 720 − 240 − 180 = 300 (10k yen) per year, the largest of the four plans, but its initial investment is also the largest at 1,250. The payback period is 1,250 ÷ 300 ≈ 4.2 years, longer than the 3.6 years of イ. This is a typical wrong-answer pattern in which you are pulled in by the large effect amount of 720, but what you should compare is not the effect amount itself but “the ratio of net effect to initial investment”.
- イ
正解 The correct answer is イ (new development, initial investment 900 (10k yen)), whose payback period of 3.6 years is the shortest of the four plans. The payback period is found by “initial investment ÷ net effect per year”. The point to be careful about here is that you must not use the effect amount as it is. Once the system is running, the operating cost and the maintenance fee go out every year, so the effect that actually stays in hand each year is “effect amount − operating cost − maintenance fee”. For イ this is 510 − 170 − 90 = 250 (10k yen) per year. Dividing the initial investment of 900 by it gives 900 ÷ 250 = 3.6 years. Applying the same calculation to the other three plans gives about 4.2 years for ア, 5.0 years for ウ, and 6.0 years for エ, so イ is the shortest. Even エ, which has the smallest initial investment (600), needs 6.0 years to pay back because its net effect is only 100 per year. The aim of this question is that you must not judge by the size of the initial investment alone.
Incorrectウ
Its net effect is 440 − 120 − 160 = 160 (10k yen) per year. Dividing the initial investment of 800 by it takes 800 ÷ 160 = 5.0 years. Although package adoption makes the initial investment 100 smaller than イ, the maintenance fee of 160 per year is heavy against the effect amount of 440, so the net effect does not grow. This is a typical case showing that package adoption can hold down the initial cost yet still end up with an expensive maintenance fee.
Incorrectエ
Its initial investment of 600 is the cheapest of the four plans, but its net effect is only 300 − 80 − 120 = 100 (10k yen) per year, so the payback period is 600 ÷ 100 = 6.0 years, the longest of the four. If you pick it just because the initial investment is the smallest, you get it wrong. Do not overlook that 200 out of the effect amount of 300 (operating cost 80 + maintenance fee 120) is eaten up by running costs.
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- Payback period of an investment = initial investment ÷ net effect per year. The net effect per year is “effect amount − operating cost − maintenance fee”, so you must always subtract the running costs that occur every year from the effect amount before dividing.
- The plan with the smallest initial investment is not necessarily the one that pays back fastest. Cost-effectiveness must be evaluated by including both the initial cost and the running costs; in this question the cheapest plan エ (600) is the longest at 6.0 years, while イ is the shortest at 3.6 years.
用語