Derangement Puzzles: How to Count Mix-Ups With Nothing in Place
How to count and solve derangement puzzles where no jar, key or tile may stay in its own place, with the counting rule, a table and a clue puzzle.
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Articles about counting puzzles
Counting and Combination Puzzles: How to Count Every Way
Learn when to multiply and when to add, how to count orderings, groups and number splits, and how to avoid double counting, with a worked puzzle.