5
4
9
7
7
2
6
4
8
9
4
1
5
1
5
9
8
6
4
9
3
3
6
8
7
3
1
9
6
6
4
9
5
2
3
Before using pencil marks, see how far you can get on a hard puzzle with pure mental tracking.
Before using pencil marks, see how far you can get on a hard puzzle with pure mental tracking.
Work the most constrained areas first — rows, columns, or boxes that already have the most filled digits.
Work the most constrained areas first — rows, columns, or boxes that already have the most filled digits.