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The Die That Cannot Exist (illustration)
FILE No.68Unsolved

The Die That Cannot Exist

Difficulty ★☆☆about 3 minTheft CaseDice facesRules
A die was swapped at a gambling den. One photo shows an impossible set of three faces.

Case Record

A die at a gambling den was swapped for a rigged one. Police studied photographs of four dice. Each photo shows the three faces visible from one corner.

  • Die A: 1, 2, 3
  • Die B: 2, 3, 6
  • Die C: 1, 4, 6
  • Die D: 4, 5, 6

On a normal die, opposite faces always add up to 7: 1 is opposite 6, 2 opposite 5, 3 opposite 4.

The three faces seen from one corner are all next to each other.

Your question

Which die shows an impossible combination?

Case Files

Evidence

Diagram

Four diceDieFacesA1, 2, 3B2, 3, 6C1, 4, 6D4, 5, 6Opposite faces always sum to 7.
Diagram

Timeline

  1. A die is swapped at the den.
  2. Police study photos of four dice.

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

What do opposite faces add up to?

Open hint 2

Can opposite faces be seen from the same corner?

Open hint 3

Look for a pair that adds to 7.

Solve It

Your question

Which die shows an impossible combination?

Choose the answer closest to the truth.

Share: I'm solving this

The Truth

Die C (1, 4, 6)

The answer is: Die C (1, 4, 6).

Faces visible from one corner are mutually adjacent, so none of them can be opposite another. On Die C, 1 and 6 add up to 7, so they are opposite faces and cannot be seen together.

Dice A, B and D have no pair adding to 7 (for B: 2+3=5, 2+6=8, 3+6=9; for D: 4+5=9, 4+6=10, 5+6=11), so they are possible.

Cannot be seen togetherDiePair summing to 7Possible?AnoneYesBnoneYesC1 and 6NoDnoneYes
Diagram of the solution

Key Points

  • Opposite faces (sum 7) can never be seen together
  • Search each set for a pair summing to 7
  • The rule-breaker is the swapped die

Why people get fooled

A set like 1, 4, 6 looks like a random, perfectly ordinary mix of numbers.

Similar tricks

  • The rule-contradiction type
  • The dice-layout type

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