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Kode #90: hints & solution

Here's the clue board for Kode #90. 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.

  • 19216▲1●1
  • 29278▲0●1
  • 36142▲1●1
  • 48035▲1●1
  • 56957▲0●0

Spoiler-free hints

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

That cracks it: the code is 3012.

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