Ordering puzzles give relationships such as before, after or immediately next to. Your job is to find an arrangement—or a necessary fact—without treating unspecified relationships as fixed.
Build the known chain
Four talks, A, B, C and D, occur in distinct time slots. A is before C. B is after C. D is before B.
The first two clues give A → C → B. The third puts D somewhere before B, but does not tell you whether D is before A, between A and C or between C and B.
Enumerate the remaining positions
The possible orders are D A C B, A D C B and A C D B. In every valid order, B is last. D's exact position varies.
If the question asks what must be true, B is last is supported. D is first is only possible, not necessary.
Immediately is an extra constraint
A before C allows intervening items. A immediately before C requires the pair to stay together. Treat that pair as a block when arranging the remaining objects, while preserving the order inside it.
Do not convert a general before clue into adjacency just because the first arrangement you imagine happens to place the objects together.
A useful method
- Write the strongest chain implied by the clues.
- Group explicitly adjacent items into blocks.
- Place fixed endpoints or excluded positions.
- Try the remaining possibilities systematically.
- Recheck every clue against the final order.
Distinguish existence from necessity
One valid arrangement proves that an order could occur. It does not prove that it must occur or that no alternative exists. To establish a necessary feature, check all remaining possibilities or derive it from the constraints. This distinction is the main reasoning task in many ordering questions, and it is easy to lose when you find a plausible arrangement quickly.