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X X X - 5 6 X - X X 8
1 8 5 - 2 3 X - 6 X 9
7 6 2 - 8 X 9 - 3 X X
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X X 9 - 1 2 8 - 7 3 X
X 3 7 - 9 X X - X 8 1
X 1 8 - X 7 3 - 9 X X
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X 7 X - X X X - 8 X 2
8 2 6 - 7 9 X - 1 X 3
X X 1 - X 8 2 - X X 7
skipper

Posts: 4
Joined: 14 February 2006

The number in the top row, column 7 must be 2 or 4. The reason is that all the other numbers can be seen from that spot, except 2 and 4.

Then, if you look in box 1 (the top-left 3x3 box), there must be a 4 in the top row, and therefore it can not be in the cell we noted earlier. That means the only candidate left is 2.

Vidar
vidarino

Posts: 295
Joined: 02 January 2006

Thank you very much, I have been studing this puzzle for 2 days, and could not see that! Thanks again.
skipper

Posts: 4
Joined: 14 February 2006

Hi skipper,
You say in your chosen subject title that you are just learning so you may wish to look at the following links (just click on them) which explain some of the techniques used for solving these puzzles. Make sure you fully understand the basic stuff (such as "naked" and "hidden" singles, pairs, triples, etc. and "Locked Candidates(1) & (2) before you get into the advanced techniques like X-Wings, Swordfish, Coloring etc.

http://www.paulspages.co.uk/sudoku/howtosolve/index.htm
http://www.angusj.com/sudoku/hints.php
http://www.simes.clara.co.uk/programs/sudokutechniques.htm