Playing Tips

Here are some techniques to help you to solve RUSH 81™ puzzles:

Hidden Single

A hidden single is the only cell in a row/column/sub-grid that can have a particular value. For example, in Figure 1, let us try to determine where 5 (yellow) should be in the GHI-456 sub-grid. There is a 5 (yellow) in G1, so if we scan down that column, we conclude that 5 (yellow) cannot go in either cell G4 or G5. There is also a 5 (yellow) in H9, so if we scan up that column, there cannot be a 5 (yellow) in either cell H6 or H5. Finally, there is a 5 (yellow) in E6, so that eliminates H6 (again) and I6. So the only cell left in the GHI-456 sub-grid is I5, so I5 must be 5(yellow). This method of “cross-scanning” to find a single cell within a sub-grid that can contain a particular value is the most important technique for beginners to learn.

Naked Single

A naked single is a cell that can only have one possible value based on the values of the other cells in the same row/column/sub-grid. For example, in Figure 2, cell D6 can only be 1 (black) because there is a 2 (brown) in the same row (G6), a 3 (red) in the same sub-grid (F5), a 4 (orange) in the same row (C6), a 5 (yellow) in the same column (D2), a 6 (green) in the same column (D8), a 7 (blue) in the same column (D7), an 8 (purple) in the same row (A6) and sub-grid (E5), and a 9 (gray) in the same sub-grid (E6).