Unit 16 · Positional Constraint Deduction
Five Chests in a Row — Which Has the Key?
Lesson 6 of 6
About this lesson
Five chests in a row, five clues, and only one chest with the key to freedom. This is the richest positional constraint puzzle in this unit — it combines "far right" anchoring, distance-based placement, "left of" ordering, and adjacency exclusions. The secret is to start with the clue that gives an absolute position (black is at far right), then chain outward to place each remaining chest.
Chapters
Question
A girl is locked in the dungeon of a castle. There are 5 chests in a row in the dungeon, one of which contains a key to escape, but the others contain poisonous snakes. The girl can only open one chest. She has 5 clues to help her make her choice:
- The white chest is 2 places away from the chest with the key.
- The black chest is at the far right and 2 places away from the white chest.
- The red chest is not next to the chest with the key.
- The yellow chest is to the left of the white one.
- The purple chest is not next to the black or white chests.
Which chest should the girl open to find the key?
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