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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

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:

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:

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