A librarian is arranging six new books—Fiction (F), History (H), Memoir (M), Poetry (P), Science (S), and Travel (T)—on a single shelf from left to right, numbered 1 to 6. The following conditions apply: * History must be placed immediately to the left of Science. * Neither Poetry nor Travel can be placed at either end of the shelf. * Fiction must be placed at position 2. * Memoir must be placed at some point after Fiction. If Poetry is placed at position 3, which of the following must be true?
- AMemoir is placed at position 5.
- BScience is placed at position 6.
- CTravel is placed at position 4.
- DHistory is placed at position 4.
Show answer & explanationAnswer & explanation
Correct answer: B. Science is placed at position 6.
Given Poetry at position 3, and Fiction at position 2, we have: _ F P _ _ _. History (H) must be immediately left of Science (S), forming the 'HS' block. Neither P nor T can be at the ends (1 or 6). If P is at 3, it's not at an end. Memoir (M) must be after Fiction (2). The remaining positions are 1, 4, 5, 6. If HS is placed, it cannot be at 1,2 (F is there), 2,3 (F,P there), 3,4 (P there). So HS must be at 4,5 or 5,6. If HS is at 4,5, then T must be at 6 (but T cannot be at an end). Therefore, HS must be at 5,6. This places Science at 6.
Why the other options are wrong
- A. Memoir could be at position 1 (as shown in the valid sequence M F P T H S), or 4. Not a must be true.
- C. Travel could be at position 4, but it could also be at other positions like 1. Not a must be true.
- D. History could be at position 5 (as shown in the valid sequence M F P T H S). Not a must be true.
Conditional Must Be True
Determining a statement that is unconditionally true under a specific 'if' premise, by analyzing all possible outcomes.
- Start with the fixed conditions and the 'if' premise.
- Exhaust all possible arrangements under these constraints.
- Identify elements whose positions are constant across all valid arrangements.
Memory trick: If this piece fits, that piece HAS to go there.