Kode #127: hints & solution

Here's the clue board for Kode #127. 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.

  • 18169▲1●1
  • 26109▲0●2
  • 39074▲0●2
  • 47851▲0●2
  • 56295▲0●0

Spoiler-free hints

  • 3 of the four digits are even.
  • The four digits add up to 13.
  • Just one digit is 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 10 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 (6 2 9 5) has no marks at all, so 6, 2, 9, and 5 are not in the code.
  2. Row 1 (8 1 6 9) has 2 marks still unexplained, and only 2 digits are left undecided: 8 and 1. So both are in the code.
  3. Row 2 (6 1 0 9) has one mark still unexplained, and only one digit is left undecided: 0. So it is in the code.
  4. Row 4 (7 8 5 1) has 2 marks, already accounted for by 8 and 1. That rules out 7.
  5. Row 3 (9 0 7 4) has one mark still unexplained, and only one digit is left undecided: 4. So it is in the code.
  6. That makes all four digits of the code: 0, 1, 4, and 8. Every other digit is out, which also rules out 3.
  7. Row 1 (8 1 6 9) has one digit in the right spot. Since row 2 rules out the 1 in position 2, it has to be the 8 in position 1.
  8. The 0 has only one spot left: position 4 (row 3 rules out position 2, row 2 rules out position 3, and position 1 is already 8).
  9. The 1 has only one spot left: position 3 (row 2 rules out position 2, position 1 is already 8, and position 4 is already 0).
  10. That leaves the 4 for position 2.

That cracks it: the code is 8410.