Naked Quad Practice Puzzles

Every puzzle below is verified to feature the Naked Quad as its hardest required technique — of the 65,284 puzzles in our library, 4,499 require it and 4,137 need nothing harder. New to the pattern? Learn the Naked Quad or see a worked example first.

How to drill the Naked Quad

Four cells in a unit whose candidates together come to exactly four digits form a Naked Quad, and those four digits can be struck from every other cell in the unit. Only a few thousand puzzles in the library genuinely require one, which tells you something useful: if you think you have found a quad, you have more often found a simpler pattern wearing a disguise.

The practical reason to drill it is that a quad is frequently the same information as a Hidden Pair viewed from the other side. In a unit with six unsolved cells, four cells holding four digits between them means the remaining two cells hold the other two — a Hidden Pair. Solvers who see both descriptions of one position stop being surprised by either.

Search the way you would for a triplet, from the union rather than from appearances: cells with four or more candidates cannot participate, so the candidate set is small.

Curated Naked Quad puzzles

  1. Practice puzzle #1 — 24 givens · needs Naked Single, Hidden Single, Naked Quad
  2. Practice puzzle #2 — 24 givens · needs Naked Single, Hidden Single, Naked Quad
  3. Practice puzzle #3 — 24 givens · needs Naked Single, Hidden Single, Naked Quad
  4. Practice puzzle #4 — 25 givens · needs Naked Single, Hidden Single, Naked Quad
  5. Practice puzzle #5 — 25 givens · needs Naked Single, Hidden Single, Naked Quad
  6. Practice puzzle #6 — 25 givens · needs Naked Single, Hidden Single, Naked Quad
  7. Practice puzzle #7 — 26 givens · needs Naked Single, Hidden Single, Naked Quad
  8. Practice puzzle #8 — 23 givens · needs Naked Single, Hidden Single, Naked Quad
  9. Practice puzzle #9 — 25 givens · needs Naked Single, Hidden Single, Naked Quad
  10. Practice puzzle #10 — 25 givens · needs Naked Single, Hidden Single, Naked Quad
  11. Practice puzzle #11 — 24 givens · needs Naked Single, Hidden Single, Naked Quad
  12. Practice puzzle #12 — 23 givens · needs Naked Single, Hidden Single, Naked Quad
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Naked Quad practice FAQ

How many Sudoku puzzles require the Naked Quad technique?
Of the 65,284 puzzles in the Precision Sudoku library, 4,499 require the Naked Quad to solve, and 4,137 can be completed with nothing harder than the Naked Quad. Every puzzle is verified by a solver that records the exact techniques needed.
Is a Naked Quad ever actually necessary?
Rarely, and that is worth knowing. Roughly 4,500 puzzles in our library require one as their hardest move. Most apparent quads dissolve into a pair, a triplet or an omission if you look again, so treat spotting one as a prompt to double-check for something cheaper first.
How is a Naked Quad related to a Hidden Pair?
They are often two readings of the same position. If four cells of a unit hold four digits between them, whatever cells remain must hold the digits left over. In a six-cell unit that leftover is a Hidden Pair, so either technique reaches the same eliminations by opposite routes.