# Solving a Sudoku Puzzle

## Presentation on theme: "Solving a Sudoku Puzzle"— Presentation transcript:

Solving a Sudoku Puzzle
By Marlene Walther ATeacherFirst.com

Rows go across … Use the numbers from 1 to 9 only!
Each row has cells across The numbers 1 to 9 will appear only once in each row There are 9 rows in a puzzle

Columns go down … Each column has 9 cells down
The numbers 1 to 9 will appear only once in each column There are 9 columns in each puzzle

Blocks … The numbers 1-9 will appear only once in each 3 x 3 block
There are 9 blocks in each puzzle

So … We have 9 columns We have 9 rows And we have 9 blocks

Step #1 Look at the three blocks on the left side of the puzzle
Notice which numbers are repeated (1, 3, 4, 7) Notice that the number 3 is in Column 1 and Column 2

Step #1 The number 3 can appear only once in each column
The number 3 is already in Column 1 and Column 2, so where will it go in Column 3? The number 3 must appear in the bottom block because it is in the top two blocks already

Step #1 The number 3 cannot appear in any column or row where it is already The number 3 cannot appear in any block where it is already It must go here – the only place left

Step #1 Write the number 3 in the cell 3

Step #2 Look at the number 1 in the three blocks on the left 3
The number 1 cannot appear in those two columns again The number 1 cannot appear in the top or bottom block 3 There is only one cell in the third column where the number 1 can go. Can you find it?

Step #2 Did you get it right? 1 3

Step #3 Look at the number 4 in the first three blocks on the left
The number 4 cannot appear in those two columns or those two blocks again 1 There is only one cell in the top block where the number 4 can go. Can you find it? 3

Step #3 4 Did you get it right? 1 3

Step #4 Look at the number 7 in the middle three blocks 4
The number 7 cannot appear in those two columns again 1 There is only one cell in the top middle block where the number 7 can go. Can you find it? 3

Step #4 4 7 Did you get it right? 1 3

Step #5 Look at the 7’s in the top three blocks and the blocks on the left 4 7 The number 7 cannot appear in any row or column twice 1 There is only one cell in the top block where the number 7 can go. Can you find it? 3

Step #5 4 7 7 Did you get it right? 1 3

Step #6 4 7 7 1 3 Notice all the 7’s in the puzzle.
There is one 7 in every block except the bottom right block 7 1 There is only one cell where the number 7 can go. Can you find it? 3

Step #6 4 Did you get it right? 7 7 1 3 7

Step #7 4 7 Where will the 4 go in this block? 7 1
Would you like a hint? 3 7

Step #7 4 7 7 1 3 7

Step #7 4 Did you get it right? 7 4 7 1 3 7

Step #8 4 Fill in the number 4 in the bottom right block
There is only one cell where it can go 7 4 7 1 3 7

Step #8 4 7 4 7 Did you get it right? 1 3 7 4

Step #9 4 There is only one possible cell for the number 3 in the bottom right block Where does the number 3 go? Would you like a hint? 7 4 7 1 3 7 4

Step #9 4 7 4 7 There is only one cell where the number 3 can go
Can you find it? 1 3 7 4

Step #9 4 7 4 7 Did you get it right? 1 3 7 3 4

Step #10 4 7 4 Where will the number 3 go in the middle block?
Would you like a hint? 7 1 3 7 3 4

Step #10 4 7 4 7 There is only one possible place for the number 3 in the middle block 1 3 7 3 4

Step #10 4 Did you get it right? 7 4 7 1 3 3 7 3 4

Step #11 4 7 4 Where will the number 3 go in the top middle block?
There is only one cell where it can go 7 1 3 3 7 3 4

Step #11 4 7 3 4 7 1 3 Did you get it right? 3 7 3 4

Step #12 4 Can you figure out where the number 2 will go in the top left block? Would you like a hint? 7 3 4 7 1 3 3 7 3 4

Step #12 4 7 3 4 7 There is only one possible cell for the number 2 in the top left block. 1 3 3 7 3 4

Step #12 4 2 7 3 4 7 Did you get it right? 1 3 3 7 3 4

Step #13 4 2 There are only two cells open in the top middle block
You can use the numbers 1-9 only once in each block Which two numbers must go in those two cells? 7 3 4 7 1 3 3 7 3 4

Step #13 4 2 The numbers 2 and 9 must go in this block
There is only one place for the number 2 Would you like a hint? 7 3 4 7 1 3 3 7 3 4

Step #13 The number 2 cannot go in the top row because there is a 2 in that row Therefore, 2 must go in the third row And then the number 9 must go in the top row (the only cell remaining in that block) 4 2 7 3 4 7 1 3 3 7 3 4

Step #13 4 2 9 You can now see that the top middle block has all the numbers from 1-9 in it Please note that no number is repeated in that block 7 3 4 7 2 1 3 3 7 3 4

Step #14 4 2 9 3 Where will the 3 go in the top right block? 7 3 4 7 2
Did you get it right? 3 7 3 4

Step #15 4 2 9 3 Where will the 5 go in the top left block? 7 3 4 7 5
Did you get it right? 3 7 3 4

Step #16 4 2 9 3 Where will the 9 go in the top left block? 7 9 3 4 7
5 2 1 3 Did you get it right? 3 7 3 4

Step #17 4 2 8 9 3 There is only one number to go in the top left block What number has not been used? 7 9 3 4 7 5 2 1 3 Did you get it right? 3 7 3 4

Step #18 4 2 8 9 6 3 There is only one number to go in the top row
What number has not been used? Did you get it right? 7 9 3 4 7 5 2 1 3 3 7 3 4

Step #19 4 2 8 9 6 3 There is only one number to go in the second row
What number has not been used? Did you get it right? 9 7 5 3 4 7 5 2 1 3 3 7 3 4

Step #20 4 2 8 9 6 3 There are two numbers that need to go in the top right block What numbers have not been used? 7 9 3 4 5 7 5 2 1 3 3 7 3 4

Step #20 4 2 8 9 6 3 The two numbers are 9 and 1 The 9 can go in only one cell because there is a 9 in one of the columns 7 9 3 4 5 7 5 2 9 1 1 3 Did you get it right? 3 7 The number 1 will go in the last cell. 3 4

Step #21 4 2 8 9 6 3 There are two numbers that need to go in this row
What two numbers have not been used? 7 9 3 4 5 7 5 2 9 1 1 3 3 7 3 4

Step #21 The 2 cannot go in the second column twice, so it must go in the 5th column 4 2 8 9 6 3 7 9 3 4 5 7 5 2 9 1 8 1 2 3 The 8 cannot go in the 5th column, so it must go in the 2nd column 3 7 3 4

Step #22 4 2 8 9 6 3 7 9 3 4 5 Fill in the missing number in this column 7 5 2 9 1 1 8 2 3 6 3 7 3 4

Step #23 4 2 8 9 6 3 7 9 3 4 5 Fill in the missing number in this column 7 5 2 9 1 1 8 2 3 6 3 7 3 9 4

Step #24 Which two numbers are missing in this column? 4 2 8 9 6 3 7 9
5 7 5 2 9 1 The number 6 can go in only one possible cell because already appears in one of the rows 1 8 2 3 6 2 3 7 3 Fill in the two numbers 9 4 6

Step #25 4 2 8 9 6 3 7 9 3 4 5 7 5 2 9 1 Fill in the missing number in this column 1 8 2 3 6 2 3 7 5 3 9 4 6

Step #26 4 2 8 9 6 3 7 9 3 4 5 7 5 2 9 1 Fill in the missing number in this block 1 8 2 3 5 6 2 3 7 5 3 9 4 6

Step #27 4 2 8 9 6 3 There are three numbers missing from this block.
Which numbers are they? Can you figure out where the 8 goes? 7 9 3 4 5 7 5 2 9 1 1 8 2 3 5 6 2 3 7 5 3 8 9 4 6

Step #28 4 2 8 9 6 3 Where does the number 1 go in this block?
There is only one place it can go. 7 9 3 4 5 7 5 2 9 1 1 8 2 3 5 6 2 What number is left to go in this block? Write it in. 3 7 5 5 3 8 9 4 1 6

Step #29 4 2 8 9 6 3 Which number is left to go in this column?
Fill it in. 7 9 3 4 5 7 5 2 9 1 1 8 2 3 5 6 2 1 3 7 5 5 3 8 9 4 1 6

Step #30 Which two numbers still need to go in this column?
The 8 can go in only one possible cell. Write it in. Then write in the last number. 4 2 8 9 6 3 7 9 3 4 5 7 5 2 9 1 1 8 2 3 5 6 9 2 1 8 3 7 5 5 3 8 9 4 1 6

Step #31 4 2 8 9 6 3 7 9 3 4 5 Which number needs to go in this row?
Write it in. 7 5 2 9 1 1 8 2 3 5 6 1 9 2 1 8 3 7 5 5 3 8 9 4 1 6

Step #32 4 2 8 9 6 3 Fill in the two numbers that must go in this row.
The number 5 can go in only one cell. The number 9 will go in the other one. 7 9 3 4 5 7 5 2 9 1 1 8 2 3 5 6 1 9 2 5 9 1 8 3 7 5 5 3 8 9 4 1 6

Step #33 4 2 8 9 6 3 7 9 3 4 5 Fill in the number that is missing in this row. 7 5 2 9 1 1 8 2 3 5 6 1 9 2 5 9 1 8 3 7 5 5 3 2 8 9 4 1 6

Step #34 4 2 8 9 6 3 7 9 3 4 5 The 2 and 6 are missing from this row.
Where will they go? 7 5 2 9 1 1 8 2 3 5 6 1 9 2 5 9 1 8 2 3 6 7 5 5 3 2 8 9 4 1 6

Step #35 4 2 8 9 6 3 Fill in the missing numbers in this row. 7 9 3 4
1 1 8 2 3 Congratulations on completing a Sudoku puzzle! 5 6 1 9 2 5 9 1 8 2 3 6 7 5 6 9 4 5 3 2 8 9 4 1 6

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