This question's explanation and your answers so far.
翌年度である X 年4月から開始されるプロジェクトのリスク対応計画を検討している。表に示される四つのリスクが想定されている場合に，対応への優先順位が最も高いと考えられるものはどれか。ここで，優先順位についてはリスクの発生確率と影響度を考慮し，また同じ優先度であるならば対応期限が迫っているリスクをできるだけ早急に対応する，という評価を行うこととする。
| リスク | 想定されるリスク顕在化の時期 | リスクの発生確率 | リスクが顕在化した場合の損失 |
|---|---|---|---|
| リスク1 | X+1年4月1日 | 0.6 | 6,000万円 |
| リスク2 | X 年7月1日 | 0.4 | 9,000万円 |
| リスク3 | X 年7月1日 | 0.1 | 1,000万円 |
| リスク4 | X+1年3月1日 | 0.5 | 7,000万円 |
Risk 1's expected loss is 0.6 × 60 million yen = 36 million yen, so it is indeed tied for the largest value. However, it materializes on April 1 of year X+1, the latest of the four, about nine months after Risk 2 (July 1 of year X). Under the condition in the question that a tie is broken in favor of the risk whose deadline is approaching, it ranks below Risk 2. Choosing it just because its probability of occurrence of 0.6 is the highest is a typical mistake; priority is judged not by probability alone but by the product of probability and impact.
正解 Priority for risk response is evaluated by “probability of occurrence × impact (amount of loss)” = expected loss. Calculating the four rows of the table: Risk 1 is 0.6 × 60 million yen = 36 million yen, Risk 2 is 0.4 × 90 million yen = 36 million yen, Risk 3 is 0.1 × 10 million yen = 1 million yen, and Risk 4 is 0.5 × 70 million yen = 35 million yen. The largest is 36 million yen, so Risk 1 and Risk 2 are tied. The question states that “if the priorities are the same, a risk whose response deadline is approaching should be addressed as soon as possible”, so we compare the times at which the risks materialize. Risk 2 is July 1 of year X and Risk 1 is April 1 of year X+1, so Risk 2 arrives about nine months earlier. Therefore the risk to be addressed first is Risk 2, and the correct answer is イ.
Risk 3's expected loss is 0.1 × 10 million yen = 1 million yen, the smallest of the four. Its time of materialization is July 1 of year X, the same as Risk 2 and the earliest of all, but an early deadline is only a secondary criterion used “when the priorities are the same”. Because the expected loss, which is the primary criterion, is smaller by an order of magnitude, it does not become the top priority.
Risk 4's expected loss is 0.5 × 70 million yen = 35 million yen, slightly below the 36 million yen of Risk 1 and Risk 2, which puts it third. Its time of materialization, March 1 of year X+1, is also among the later ones. It is tempting to pick it because the loss of 70 million yen is larger than 60 million yen, but the comparison must be made with the expected loss obtained by multiplying by the probability of occurrence, not with the loss amount alone.