SUDOKU #14  
 
I'm going to repeat the info at the top of Sudoku #1, just in case you haven't seen that one yet.  
I've been doing Sudoku for a while. There are a lot of people like me who have figured out some tricks or techniques that help them complete the puzzles. This page is not really for them. I met a woman recently who was just starting to try to do Sudoku. This page is for people like her. I'm not saying that I know every single trick, but I know enough to complete most puzzles.  
The basic rules of Sudoku are that there is only one of each number in each row, column, and 9 square grid. There isn't any mathematics or arithmetic. If you know how to count from 1 to 9, then you can do these puzzles. All of the techniques are based on this rule.  
Here is a sample Sudoku puzzle. It might be good to just print out this grid and write in the numbers as I go. There may be times when I do more numbers in one step than can be followed just by looking at the webpage.  
9  2  
9  6  4  5  
8  4  3  6  
4  6  5  2  
2  1  7  5  
6  2  5  8  
7  1  
This is a Evil difficulty puzzle (harder than Hard), and it will allow me to show some examples of a few of the tricks that I've uncovered. I've added the letters below to the rows and columns in order to talk about each of the 81 squares. As a convention, I will talk about squares and boxes. There are 81 squares, but there are 9 boxes of 9 squares.  
A  
B  9  2  
C  9  6  4  5  
D  8  4  3  6  
E  4  6  5  2  
F  2  1  7  5  
G  6  2  5  8  
H  7  1  
I  
J  K  L  M  N  O  P  Q  R  
There is a 6 in FJ (because of DP, EM, and GK). The numbers missing from box DMFO are 2, 8, and 9. There is a 2 in DN (because of FL and EP). There is a 2 in AO (because of GM, DN, and BQ). There is another 2 in CJ (because of AO, BQ, and FL), and another one in IK (because of CJ and FL). The final 2 is in HR (because of BQ, EP, GM, and IK).  
A  2  
B  9  2  
C  2  9  6  4  5  
D  8  4  2  3  6  
E  4  6  89  5  2  
F  6  2  1  89  7  5  
G  6  2  5  8  
H  7  1  2  
I  2  
J  K  L  M  N  O  P  Q  R  
There is a 7 and a 9 in DJ and EJ (because of CK and HK), so the numbers missing from column K in box DJFL are a 1, 3, and 5. But there is a 1 in FM and a 5 in FP, so there is a 3 in FK, a 1 in EK (because of EO), and the 5 goes in DK.  
A  2  
B  9  2  
C  2  9  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  6  2  5  8  
H  7  1  2  
I  2  
J  K  L  M  N  O  P  Q  R  
There is a 9 in AM (because of CK, BP, and ENFN). There is a 5 in BM (because of CQ, EO, and GN). There is another 5 in IR (because of CQ, FP, and GN). So there is a 5 in HJ (because of GN and IR) and another 5 in AL (because of BM, CQ, DK, and HJ).  
A  5  9  2  
B  5  9  2  
C  2  9  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  6  2  5  8  
H  5  7  1  2  
I  2  5  
J  K  L  M  N  O  P  Q  R  
There is an 8 in IJ (because of GQ and DL). There is a 6 in BL (because of CN, GK, and FJ). There is another 6 in AR (because of GK, DP, BL, and CN). There is a 4 in GJ (because of EL).  
A  5  9  2  6  
B  6  5  9  2  
C  2  9  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  4  6  2  5  8  
H  5  7  1  2  
I  8  2  5  
J  K  L  M  N  O  P  Q  R  
There is a 7 in CL (because of HK and DJEJ), and there is another 7 in IM (because of CL, FO, and ANBN).  
A  5  9  2  6  
B  6  5  9  2  
C  2  9  7  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  4  6  2  5  8  
H  5  7  1  2  
I  8  2  7  5  
J  K  L  M  N  O  P  Q  R  
The number missing from column N are 1, 3, 4, and 7, but there is a 1 and 7 in row H. So there is either a 3 or a 4 in HN. The numbers missing from column P are 1, 3, 4, 7, and 8, but there is a 1 and a 7 in row H, and there is an 8 in GQ. So HP has to be either a 3 or a 4. So there cannot be a 3 in HM. Therefore, an 8 has to be in HM and a 3 in CM.  
A  5  9  2  6  
B  6  5  9  2  
C  2  9  7  3  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  4  6  2  5  8  
H  5  7  1  8  34  34  2  
I  8  2  7  5  
J  K  L  M  N  O  P  Q  R  
There has to be either a 3 or a 4 in IN (because of CM and CO), so there has to be a 1 or a 7 in AN and BN. Therefore, there is an 8 in BO.  
A  5  9  17  2  6  
B  6  5  17  8  9  2  
C  2  9  7  3  6  4  5  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  4  6  2  5  8  
H  5  7  1  8  34  34  2  
I  8  2  7  34  5  
J  K  L  M  N  O  P  Q  R  
There is an 8 in AK (because of IJ and BO), and a 4 is in BK. There is an 8 in CP (because of GQ), and a 1 is in CR.  
A  8  5  9  17  2  6  
B  4  6  5  17  8  9  2  
C  2  9  7  3  6  4  8  5  1  
D  79  5  8  4  2  3  6  
E  79  1  4  6  89  5  2  
F  6  3  2  1  89  7  5  
G  4  6  2  5  8  
H  5  7  1  8  34  34  2  
I  8  2  7  34  5  
J  K  L  M  N  O  P  Q  R  
There is a 1 in DQ (because of CR, EK, and FM). There is a 4 in FR (because of BK, GR, EL, and DM). There is an 8 in FN (because of GQ), a 9 in EN and FQ). So there is a 7 in EJ and a 9 in DJ, and there is a 7 in DR.  
A  8  5  9  17  2  6  
B  4  6  5  17  8  9  2  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  
F  6  3  2  1  8  7  5  9  4  
G  4  6  2  5  8  
H  5  7  1  8  34  34  2  
I  8  2  7  34  5  
J  K  L  M  N  O  P  Q  R  
The number missing from row E are a 3 and an 8. There is an 8 in ER and a 3 in EQ. The numbers missing from row H are a 6 and a 9, so the 9 is in HO (because of FQ), and the 6 is in HQ.  
A  8  5  9  17  2  6  
B  4  6  5  17  8  9  2  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  3  8  
F  6  3  2  1  8  7  5  9  4  
G  4  6  2  5  8  
H  5  7  1  8  34  9  34  6  2  
I  8  2  7  34  5  
J  K  L  M  N  O  P  Q  R  
There is a 9 in GR (because of BP and FQ) and a 3 in BR. There is a 9 in IL (because of GR and HO) and a 3 in GL.  
A  8  5  9  17  2  6  
B  4  6  5  17  8  9  2  3  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  3  8  
F  6  3  2  1  8  7  5  9  4  
G  4  6  3  2  5  8  9  
H  5  7  1  8  34  9  34  6  2  
I  8  2  9  7  34  5  
J  K  L  M  N  O  P  Q  R  
The numbers missing from box APCR are the 4 and the 7, so there has to be a 7 in BN and a 1 in AN. So there is a 1 in BJ (because of AN) and a 3 in AJ.  
A  3  8  5  9  1  2  6  
B  1  4  6  5  7  8  9  2  3  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  3  8  
F  6  3  2  1  8  7  5  9  4  
G  4  6  3  2  5  8  9  
H  5  7  1  8  34  9  34  6  2  
I  8  2  9  7  34  5  
J  K  L  M  N  O  P  Q  R  
The numbers missing from column O are a 1 and a 6, but there is a 6 in GK. So the 6 is in IO and the 1 is in GO. Therefore, there is a 1 in IP.  
A  3  8  5  9  1  2  6  
B  1  4  6  5  7  8  9  2  3  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  3  8  
F  6  3  2  1  8  7  5  9  4  
G  4  6  3  2  5  1  8  9  
H  5  7  1  8  34  9  34  6  2  
I  8  2  9  7  34  6  1  5  
J  K  L  M  N  O  P  Q  R  
The numbers missing from row I are a 3 and a 4, but there is a 3 in EQ. So there is a 4 in IQ, a 3 in IN, a 4 in HN, and a 3 in HP. There is a 7 in GP, a 4 in AP, a 7 in AQ.  
A  3  8  5  9  1  2  4  7  6  
B  1  4  6  5  7  8  9  2  3  
C  2  9  7  3  6  4  8  5  1  
D  9  5  8  4  2  3  6  1  7  
E  7  1  4  6  9  5  2  3  8  
F  6  3  2  1  8  7  5  9  4  
G  4  6  3  2  5  1  7  8  9  
H  5  7  1  8  4  9  3  6  2  
I  8  2  9  7  3  6  1  4  5  
J  K  L  M  N  O  P  Q  R  
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