by **Shazbot** » Mon Oct 31, 2005 10:01 pm

A "group" is any row, column, or 3x3 box. There are 27 groups on a standard 9x9 sudoku grid - 9 rows, 9 columns, 9 3x3 boxes - each group must contain the numbers 1-9 once and only once.

You have a few moves available.

A "hidden single" in column 8 - there's only one place for the 1 to go, so it must go there.

"naked pairs" - if two cells within a single group contain ONLY the same two candidates, regardless of whether those candidates appear within other cells in that group, then they MUST go in those two cells. So you can eliminate them from the other cells in that group. In column 5, you have 2 cells with 3 and 7 and nothing else. So 3 and 7 can be eliminated from the rest of the cells in column 5. If you have all your candidates filled in (which you will have if you're using Simple Sudoku), you'll see this leads to another naked pair of 1 and 3 in row 5, so you can remove 1 and 3 from all the other cells in row 5, leaving you with a 5 in r5c5.

There are a few more hidden singles and naked pairs that should allow you to progress.