How to solve sudoku 3 of 6

Pairs, triples and quads

Two squares that together claim exactly two digits keep those digits occupied for the rest of their group — even if you don’t know yet which digit goes where. The same idea works with three and with four, and it works both ways: naked (look at the squares) and hidden (look at the digits).

Naked pair

Two squares in the same group both have exactly the same two candidates. Which goes where you don’t know, but together they lock up both digits — so no other square in that group can use them.

If "3 or 8" appears twice in the same row, the 3 and the 8 of that row are taken: you can cross them out in all the other squares of the row.

Hidden pair

Within a group, two digits only fit in the same two squares. Those two squares then belong to those two digits, so all other candidates in those squares drop out — even if there are still five little numbers in them.

Naked triple

A naked pair, but with three squares that use exactly three candidates between them. Each square doesn’t have to hold all three: if the three together use no more than three digits, those digits are used up for the rest of the group.

Hidden triple

Three digits only fit in the same three squares of this group. Those squares then belong to those three digits, so everything else in those squares can go.

Naked quad

Four squares in one group use exactly four candidates between them. Those four digits are spread over those four squares, so the rest of the group loses them.

Hidden quad

Four digits can only go in the same four squares of this group. Those squares then belong to those four together and keep nothing else.

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