Logic Puzzles for Adults

Types of logic puzzles

Every logic puzzle works the same way at heart: the clues are true, and if you connect them carefully, you reach the only possible answer without guessing. What changes from type to type is what you’re connecting.

• Logic grid puzzles. You match several categories, such as people, places and times. A clue like “Anna wasn’t at the movies” goes straight into a grid. Tip: mark every pairing you rule out, not just the matches. Ruling things out is what leaves a single option in the end.
• Line-up puzzles. A variation of the logic grid where things stand side by side, like houses on a street or seats at a counter. Clues such as “directly left of” or “not on the end” come into play. These are often called Einstein puzzles. Tip: check the ends of the row first, since many clues rule them out.
• Number logic like sudoku. Digits in a grid, each exactly once per row, column and box. No arithmetic is involved. Tip: pick one row, column or box and ask where each missing digit can still go.
• Crime logic. The clues are suspects’ statements, and the question is who was where, and when. One version is a floor plan where you place people on a map of the house by fixed rules. Tip: read every statement as a fact and start with whoever has the fewest options.

Try it: four friends at the café counter

Four members of a puzzle club sit side by side at a café counter, on stools 1 to 4, counted from the left. Each of them orders a different dessert: apple pie, cheesecake, carrot cake or pecan pie. Who sits where, and who has which dessert?

1. Henry sits directly to the right of Grace.
2. Lucy doesn’t sit next to Henry.
3. Lucy has the cheesecake.
4. Whoever has the apple pie sits directly to the left of Grace.
5. Henry doesn’t have the pecan pie.

How to solve logic puzzles: grid, elimination, contradiction

• Work in a grid. List the categories along the edges and mark every pairing: X for “no”, a dot for “yes”. Once you place a dot, the rest of that row and column in the same category gets an X.
• Enter direct clues first. Statements like “Lucy has the cheesecake” go in right away. Then turn to the clues that only reveal something in combination with others.
• Check the edges. Clues like “directly left of” often rule out the end positions. In the example, that was step one.
• Look for a contradiction. When two options remain, assume one and follow it through. If something breaks, the other option is right. Mark assumptions in pencil or a different color so you can erase them.
• Reread the clues. A clue that tells you nothing at the start often pays off later, once more is settled.

Choosing the right difficulty

To start, pick small puzzles with three or four people and two categories, like the one above. Puzzles get harder with more categories, more people and more indirect clues such as “not next to” or “somewhere left of”. You’ve found your level when you keep making progress but now and then have to test an assumption.

With sudoku, difficulty depends mostly on the size of the grid and on which techniques you need. A 4×4 or 6×6 sudoku is quick to learn, while a 9×9 grid can keep you busy for a long time.

Logic puzzles as crime stories: sudoku plus floor plan

Sudocrime turns two kinds of logic puzzles into one crime story. Every chapter comes with a sudoku. Then you place the suspects on a floor plan by one fixed rule: each row and column holds exactly one person. Every card is true, the square left free belongs to the victim (in the practice case, to a missing key), and you’re looking for the one suspect in the same room. You never have to guess. Each story shows its difficulty in magnifiers.

The practice case teaches the rules with a 4×4 sudoku and a small plan. “Silence at Lindenrain” has six chapters with 6×6 sudoku puzzles. Both cases come with the app, and you can solve a case online in your browser right now, with nothing to install. The floor plan rules explain how the plan works, and for a short case to crack yourself, try murder mystery puzzles.