Triples and quads

Expert

Triples and quads are pairs with more cells: three cells in a row, column or box that hold only three digits between them, or four with four. Triples are an Expert technique, quads a Master one.

Naked triple

Three cells whose notes, put together, are just three digits will hold exactly those three digits. Each cell doesn’t need all three: 1 7, 7 9 and 1 9 make a triple too. So those digits go from every other cell in the unit.

146717167141471478178141681681817174748897912132312471713419237932598239655947325243896698571423234968571532169657848651A2B3C4D5E6F7G8H9I
In row I, I3, I5 and I9 hold only 1, 7 and 9 between them (no cell needs all of them). Those three digits fill those three cells, so the 1s in I2 and I4 and the 7 in I2 go.

Hidden triple

Three digits that fit only in the same three cells of a unit fill those cells, so the cells’ other notes go.

12671627147141371317235241413252534142513141417251471512416714647251713512398358652494592836177698981532476678982536799386981A2B3C4D5E6F7G8H9I
In row I, 2, 3 and 5 fit only in I5, I7 and I9. Those cells must hold them, so their other notes go: the 1s in I9 and I7.

Quads

Four cells holding four digits between them, or four digits with only four places, work the same way. They’re rare, and need a Master puzzle, but when nothing else works they’re worth checking.

494937372727565647471215457945794676724254574573472371425142512478134757925756756148592342783757925768569236812559438721631948362158983968168397141A2B3C4D5E6F7G8H9I
In row H, H3, H5, H6 and H8 hold only 5, 6, 7 and 9 between them (no cell needs all of them). Those four digits fill those four cells, so the 7s in H1, H2 and H4 and the 5 in H4 go.

How to spot them

  • Look in units with many empty cells and short notes: cells with two or three notes are the building blocks.
  • If a unit has a naked triple, its other empty cells may form a hidden one, and the other way round: the two always come in pairs.

Try it on a real puzzle

Expert puzzles in Sudoku Knockout need techniques like this one, and never a guess. When you’re stuck, a hint shows you the step.

Play an Expert puzzle