A research team is studying the migratory patterns of five bird species: Falcon (F), Gull (G), Hawk (H), Ibis (I), and Jay (J). Each species migrates during a distinct month from May to September. The following conditions apply: 1. The Falcon migrates in July. 2. The Ibis migrates before the Jay. 3. The Gull migrates immediately after the Hawk. 4. Neither the Hawk nor the Jay migrates in May. Which of the following is a complete and accurate list of the months in which the Ibis could migrate?
- AMay, June
- BJune, August
- CMay, June, August
- DMay, June, August, September
Show answer & explanationAnswer & explanation
Correct answer: A. May, June
Months are May, June, July, August, September. F is in July. H-G is a block. H, J not in May. I before J. If I is in May, J could be in June, Aug, or Sep. This is possible. If I is in June, J could be in Aug or Sep. This is possible. If I is in August, J must be in September. But the H-G block needs two consecutive slots, and H cannot be in May. If I is in August, and J is in September, this leaves May, June for H-G (H in May, G in June), but H cannot be in May. So I cannot be in August. Thus, Ibis can only migrate in May or June.
Why the other options are wrong
- B. Ibis cannot migrate in August because it would force Hawk into May, which is prohibited.
- C. Ibis cannot migrate in August, making this list inaccurate.
- D. Ibis cannot migrate in August or September, making this list inaccurate.
Exhaustive Possibility Listing (Months)
Identifying all possible positions or values an item can take, given a set of ordering and grouping rules over a fixed sequence (e.g., months).
- Requires systematically testing each potential position for the target item.
- Each tested position must lead to at least one fully valid arrangement.
- Process of elimination for positions that violate any rule is crucial.
Memory trick: Months are fixed, birds fly free (mostly).