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Kode #129: hints & solution

Here's the clue board for Kode #129. 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.

  • 15812▲1●1
  • 28612▲0●2
  • 37394▲0●2
  • 43641▲1●0
  • 59461▲0●0

Spoiler-free hints

  • 2 of the four digits are even.
  • The four digits add up to 20.
  • 2 of the digits are 5 or higher.

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

That cracks it: the code is 3827.

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