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Only a brave person
is willing to honestly admit,
and fearlessly to face,
what a sincere and
logical mind discovers.
Rodan of Alexandria - 64AD
Egyptian philospher

Cooperative learning series

Sudoku 数独 basic strategies 1

After you have completed the basic exercise above,
here is another strategy to consider.
The possibilities (in green) for nines in the fourth row are in the last two cells

7 9 2 4
5 6
2 9
4

1 6
7

3 2 8 1 6
5 1 6
7 9
1 6
7 9
9 . 9 . 9 .
9 . 9 . 9 .
9

Because you must have a nine in the fourth row in the shaded box,
you cannot have a nine in the other rows of that shaded box (the red nines).

Another strategy:
What can you guess about the middle rows of the two shaded boxes?
Again, the possibilities for the middle row of the middle box are in green:

5

6 1 8 5
2 5
2 5
9
2 9
2 7 3 4 6

Answer:
What can you guess about the middle rows of the two shaded boxes?
Again, the possibilities for the middle row of the middle box are in green:

5

6 1 8 7
9 9 9 2 5
2 5
9
2 9
2 5
9
2 5
9
2 5
9
2 7 3 4 6

Answer:
In the middle box, only three numbers 2 5 9 are possible, and there are only three spaces available. Therefore, those possibilities are not possible in the spaces in the rows of the other boxes.

Since there already is a 5 and 2 in the left-hand box, that eliminates 2 and 5 in the middle row. 9 is not possible in its middle row since a nine must be in that row of the middle box..

In the right-hand shaded box, all three 2 5 9 are not possible in the middle row and must be options in its empty spaces.

Websites on Sudoku:

What's a Pappacom puzzle? What are symmetrical clues?
Computer-generated or hand-constructed puzzles?

  1. Wikipedia
    All about Sudoku, strategies, etc.
  2. Natural Maths Sudoku
    Use Microsoft Excel to help you learn to solve Sudoku
  3. Websudoku:
    "Billions" to work online, four levels of difficulty,
    with checking feature
  4. Sudoku . com. au
    Australian Sudoku solving on line with a picture for a reward!

Math series

Math exams | Solving linear equations | Solving math word problems, introdution |
Word problems, exercise I | Word problems, II | Word problems, III |
Evaluating algebraic expressions | Creating and developing spreadsheets |
P.E.M.D.A.S.: 2nd exercise | P.E.M.D.A.S.: 3rd exercise | Sudoku 数独

Flash exercise contributed by Matt Schiller and Dr. Brad Hokanson, Interactive Media (DHA 4384) School of Design, University of Minnesota.