Solving a Sudoku Puzzle

# Solving a Sudoku Puzzle

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## Solving a Sudoku Puzzle

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1. Solving a Sudoku Puzzle By Marlene Walther

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

3. 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

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

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

6. 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

7. 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

8. 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

9. Step #1 • Write the number 3 in the cell 3

10. Step #2 • Look at the number 1 in the three blocks on the left • 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?

11. Step #2 • Did you get it right? 1 3

12. 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

13. Step #3 4 • Did you get it right? 1 3

14. Step #4 4 • Look at the number 7 in the middle three blocks • 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

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

16. Step #5 4 • Look at the number 7’s in the top three blocks and the blocks on the left 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

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

18. Step #6 4 • Notice all the 7’s in the puzzle. 7 • 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

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

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

21. Step #7 4 7 7 1 3 7

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

23. Step #8 4 • Fill in the number 4 in the bottom right block • It can only go in one cell 7 4 7 1 3 7

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

25. 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

26. Step #9 4 7 4 7 • It can only go in one cell. • Can you find it? 1 3 7 4

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

28. 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

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

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

31. Step #11 4 7 4 • Where will the number 3 go in the top middle block? • It can only go in one cell. 7 1 3 3 7 3 4

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

33. 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

34. 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

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

36. 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

37. 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

38. 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 left in that block) 4 2 7 3 4 7 1 3 3 7 3 4

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

40. Step #14 4 2 9 3 • Where will the 3 go in the top right block? 7 3 4 7 2 1 3 • Did you get it right? 3 7 3 4

41. Step #15 4 2 9 3 • Where will the 5 go in the top left block? 7 3 4 7 5 2 1 3 • Did you get it right? 3 7 3 4

42. 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

43. 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

44. 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

45. 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? 5 7 9 3 4 7 5 2 1 3 3 7 3 4

46. 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

47. Step #20 4 2 8 9 6 3 • The two numbers are 9 and 1 • The 9 can only go in 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

48. 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

49. 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 1 8 2 3 • The 8 cannot go in the 5th column, so it must go in the 2nd column 3 7 3 4

50. 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