dailysudoku.com

[mhaverstick]

I am playing the April 26 Soduku and became stuck. I did not know the next play and ask for hint. They gave me a 5 in row 3 position 8.

Why is 5 in row 3 position 8 the next logical play? Can anyone help me?

_ _ 8 | 4 _ _ | 9 _ 6
_ 4 _ | 9 _ _ | _ _ 7
_ _ 9 | 2 3 _ | _ _ 4
-----------------------
_ _ _ | 1 6 4 | _ 9 5
4 9 _ | _ _ _ | 6 1 8
1 6 _ | _ 9 _ | _ 4 _
-----------------------
5 _ _ | _ 4 9 | _ 6 _
9 _ 4 | _ _ _ | 5 8 _
3 _ _ | _ _ 5 | 4 _ 9

[TKiel]

Mhaverstick,

Your puzzle as posted is invalid, which could just be a mis-entered number. The 6 in r7c8 can't be there.

[TKiel]

R3c8 is a naked single.

[mhaverstick]

TKeil

You are right about the 6. I was working the puzzle and put the 6 in r7c8 but I can not tell you why. How did you know that? If you can't tell I am new to Sudoku.

What does R3c8 is a naked single mean?


_ _ 8 | 4 _ _ | 9 _ 6
_ 4 _ | 9 _ _ | _ _ 7
_ _ 9 | 2 3 _ | _ _ 4
-----------------------
_ _ _ | 1 6 4 | _ 9 5
4 9 _ | _ _ _ | 6 1 8
1 6 _ | _ 9 _ | _ 4 _
-----------------------
5 _ _ | _ 4 9 | _ _ _
9 _ 4 | _ _ _ | 5 8 _
3 _ _ | _ _ 5 | 4 _ 9

[Angel]

If you go through the possibilities for R3C8, you will find there is only one
number that can go there. Every other number is already taken in row 3, column 8 or box 3.

This is a naked single.

[Robert Ferre]

I'm a newbie, too. What I have learned about naked singles in that you need to keep checking, as you add more numbers to the puzzle. When I am stuck, I go through each cell and look for what numbers are already present in that cell, row and column. Iwrite down the remaining possibilities in each cell. Sometimes I have left one that should have been deleted, leading me to think there were more possibilities than was actually true.

There is another type of single that I have also found, although your case isn't an example. Sometimes several numbers can be in a cell, but for one of those numbers it is the only possibility. For this reason I keep checking periodically the columns or rows across the puzlle. Here's how. Let's say we have the right side three squares (top right, middle right, bottom right). Let's say the number is 5. If we have a 5 in column 9 in the lower right square, and in column 7 in the middle right square, we know it must be in column 8 in the upper right square. There may be a unique cell which is the only place it will go, even though that cell may also have a 2 and a 7 marked in it as other possibilities. Eventually those possibilities would be removed, and it would become a naked single, but this is earlier in the solution. Naked singles work a little later, when more numbers are present. If you put all of the possible numbers in each cell, and faithfully erase them when those numbers are placed and eliminated as possibilities, you will eventually get down to a single number, showing you that it is, indeed, a naked single.

[TKiel]

Robert Ferre,

This is a hidden single.

Mhaverstick,

The links below contain information on basic techniques for solving Sudoku:

www.angusj.com/sudoku/hints.php

www.scanraid.com/BasicStrategies.htm

www.sadmansoftware.com/sudoku/techniques.htm

[mhaverstick]

thank you both for all the help. The websites are very helpful.

cheers