Sudoku

Last week, I started teaching the students how to solve Sudoku puzzles. Some students were already familiar with Sudoku, but many were not. If you are, you may know how many newspapers print Sudoku puzzles, how many Sudoku books there are, and how many websites dedicated to solving them exist. If not, I hope you see how the logic used to solve Sudoku puzzles is an important mathematics skill. And it's fun.

Since some students had solved Sudoku puzzles before, we shared some strategies. I include these below. Some of these are my ideas, come from books, or were suggested by the students.

• Sudoku is a logic puzzle. No mathematics computation is required.
• There is only one correct solution for each Sudoku puzzle.
• Don’t guess. There is only one number that can correctly go in each square. If you’re not absolutely sure which number goes there, leave it blank. Guessing will send you down the path to an incorrect solution.
• Be careful. If you make a mistake in one square, it will cause you to make other mistakes. Be thorough in checking that you placed the correct number in each square.
• Use the one-choice method. Look at a column, row, or 3x3 box. Does it have just one square blank? The missing square must be the one digit from 1 to 9 that’s not there. Example: If a column has 1, 2, 3, 4, 6, 7, 8, and 9, then the blank square in that column must be 5. Note: this strategy can be used in other ways.
• Use the frequency of numbers to help you. If a new puzzle has five 3s, but only two 9s, then you might start with trying to fill in more 3s.
• If you fill in a square with a number, say a 7, then see if that will help you find more 7s.
• Mark possibilities in the corners of squares. If a row, column, or 3x3 box has two blank squares, but you can’t use the one-choice method, you might consider using this hint to help you. For example, if a row is missing 4 and 6, but you don’t have enough clues to place them without guessing, then pencil a small 4 and a small 6 in the corner of each square. When you have more clues, go back and place your 4 and 6 in the correct squares.

We did a Practice problem together as a teaching example, and then students were to finish puzzle One by last Friday. This week, students have puzzles Two and Three to finish by Friday.