# Use a Pencil: Sudoku Tips

The secret to solving Sudoku is that there is no secret.

Puzzling out the numbers game is a matter of using your noggin's natural talents and the basic principles of logic: process of elimination, inference and (unless you're a purist) the occasional wild guess.

And the tips that some how-to books offer are often just codified versions of the basic strategies most players figure out on their own.

Nevertheless, here are a few pointers, courtesy of Lori Lambertson, a San Francisco math and science teacher who holds classes on playing Sudoku:

1. Use a pencil with an eraser.

2. One technique is to see which numbers appear most frequently — there's usually one that appears more often than the others. If you have a lot of fives, for example, there's a pretty good chance you'll be able to place most or all of the fives in each of the nine sub-grids. Fill in as many of the most common numbers as you can, then move onto the next-most frequent, and
so on.

3. A separate technique is to look at each sub-grid, row or column and see which is missing the fewest filled-in numbers, then work to fill in the rest of that sub-grid, row or column.

4.Feeling like you're at a dead end? This is when you thank heaven you used a pencil with an eraser.

“When you are really feeling stumped, you have to eventually put in pencil all the possibilities for each square,” Lambertson said. “You can't do Sudoku puzzles as if you could do them in pen. Being meticulous about what the possibilities are will solve most up-to-moderate-level puzzles.”

5. Now it gets complicated. Advanced strategies include concepts called “twins” or “duals” — two boxes in one sub-grid, row or column that can only contain two numbers — and “triples.” Sudoku Web sites and Internet forums can fill you in from here.

Click here to try a sample puzzle at WebSudoku.com