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SUDOKU

The object of this number game is to place the digits 1 to 9 in each 3 x 3 box in such a way that the numbers 1 to 9 also appear in each row and column of the large 9 x 9 grid. The levels of difficulty can vary from fairly straight forward to fiendishly difficult.

SUDOKU In the more difficult puzzles there are many occasions when two or more possible numbers can go in each cell and you will usually have to pencil these possibilities in, in small writing before deciding which goes where later. Before this stage there are always some cells that can have a single solution. It is better to try and find all these solutions first, before moving on to cells that have multiple possible solutions

Tips for solving SUDOKU The squares indicated in red cannot contain a 2, hence we have our first solution We will look at the puzzle shown which gives us 28 completed cells and discuss some of the methods of finding the numbers that go in some of the blank cells.

SUDOKU A similar situation occurs with the highlighted 8’s forcing our second solution

SUDOKU Row 2 needs an 8 but it can’t go in the red cells

SUDOKU Row 2 needs a 9 and a 4 but a 4 cannot go here so we have 2 more solutions

SUDOKU

Trickier situations 3 7 In this 3 x 3 box there are two cells that are not filled in as they could take either a 3 or a 7. How can we decide? 3 3 These 3’s hold the key. 3 7 This forces the entry in this cell to be a 7 and the other to be a None of these red cells can be a 3, thus forcing the remaining cell to be a 3. 3

SUDOKU Trickier situations. In this 3 x 3 box there are two cells that are not filled in as they could take either a 3 or a 7. How can we decide? 3 3 These 3’s hold the key. This forces the entry in this cell to be a 7 and the other to be a None of these red cells can be a 3, thus forcing the remaining cell to be a 3.

Puzzle Fairly EasyPuzzle 1 Solution > Getting Started Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 38 start numbers Worksheets >

Fairly EasyPuzzle 1 Puzzle 2 > Getting Started Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 38 start numbers

Puzzle 2 MediumPuzzle 2 Solution > Getting Started Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 35 start numbers

MediumPuzzle 2 Puzzle 3 > Getting Started Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 35 start numbers

Puzzle 3 HarderPuzzle 3 Solution > Getting Started Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 31 start numbers

HarderPuzzle Getting Started Telegraph > Usually a sudoku becomes trickier when less “start numbers” are given but don’t take this as a general rule. There are also hard sudoku’s with many start numbers given, and easy ones with only a few start numbers given. 31 start numbers

Telegraph Puzzle ModerateDaily Telegraph Puzzle Solution > Generally, Sudoku puzzles in daily newspapers are harder than the three introductory ones given earlier. As the puzzles increase in difficulty you may wish to learn other strategies to help you solve them. You can download a “solving sudoku document” at: It is not unusual to spend ½ to 2 hours on some puzzles. 26 start numbers

ModerateDaily Telegraph Puzzle Generally, Sudoku puzzles in daily newspapers are harder than the three introductory ones given earlier. As the puzzles increase in difficulty you may wish to learn other strategies to help you solve them. You can download a “solving sudoku document” at: It is not unusual to spend ½ to 2 hours on some puzzles. 26 start numbers

Number of Solutions How many ways are there of filling a blank 9 x 9 grid with the numbers 1 to 9 according to the rules of the game? In other words how many solutions are there? Some Sudoku Questions

How many ways are there of filling a blank 9 x 9 grid with the numbers 1 to 9 according to the rules of the game? In other words how many solutions are there? Solution Mathematicians have shown that there are: 6,670,903,752,021,072,936,960 (6.67×10 21 ) different solutions. Some Sudoku Questions

Minimum Entries What is the smallest number of cell entries that a puzzle can have so that it yields a unique solution. Some Sudoku Questions start numbers “At the moment, there are examples of 17-hint uniquely completable Sudoku puzzles, but no known 16-hint examples. Hence I am collecting as many 17-hint examples as possible, in the hope that their analysis will yield some insight. Currently I have a collection of distinct Sudoku configurations with 17 entries”. Gordon Royle, The University of Western Australia

Worksheet Fairly Easy Medium Harder Daily Telegraph (Moderate)