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Kode #15: hints & solution

Here's the clue board for Kode #15. Start with the spoiler-free hints. If you're still stuck, the full step-by-step solution is below, hidden until you open it.

The clue board

Each row is a guess that's already been graded. ▲ means a right digit in the right spot; ● means a right digit in the wrong spot.

  • 12735▲1●1
  • 26705▲0●1
  • 38470▲0●2
  • 48235▲0●2
  • 51789▲0●0

Spoiler-free hints

  • 3 of the four digits are even.
  • The four digits add up to 9.
  • Every digit is below 5.

Try the hints first. The solution below walks through every deduction.

Step-by-step solution

Every Kode can be cracked by pure deduction, with no guessing. This board falls in 8 logical steps. Open the solution to follow them one at a time.

Show the solution · reveals the code

When a row "rules out" a position, it shows that digit there but its ▲ marks are already used up (or it has none), so the digit can't sit there.

  1. Row 5 (1 7 8 9) has no marks at all, so 1, 7, 8, and 9 are not in the code.
  2. Row 3 (8 4 7 0) has 2 marks still unexplained, and only 2 digits are left undecided: 4 and 0. So both are in the code.
  3. Row 2 (6 7 0 5) has one mark, already accounted for by 0. That rules out 6 and 5.
  4. Row 1 (2 7 3 5) has 2 marks still unexplained, and only 2 digits are left undecided: 2 and 3. So both are in the code.
  5. Row 1 (2 7 3 5) has one digit in the right spot. Since row 4 rules out the 3 in position 3, it has to be the 2 in position 1.
  6. The 0 has only one spot left: position 2 (row 2 rules out position 3, row 3 rules out position 4, and position 1 is already 2).
  7. The 3 has only one spot left: position 4 (row 4 rules out position 3, position 1 is already 2, and position 2 is already 0).
  8. That leaves the 4 for position 3.

That cracks it: the code is 2043.

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