## Completely stuck and in need of help please.

Advanced methods and approaches for solving Sudoku puzzles

### Completely stuck and in need of help please.

Despite spending a good few hours on the very hard puzzle shown below, I'm stumped as to how proceed. Can anyone more skilled in the art of completing very hard Sudoku puzzles kindly point me in the right direction with a small clue? I suspect there is an X-wing somewhere but I can't see it for looking.

Thanks in anticipation.

Zeb

PS I manage to complete 1 in 3 very hard puzzles but this one is beyond me!

*** *** 725
**7 *** *4*
*5* 3*7 **1

581 94* *37
*** *8* *5*
*4* *53 8**

375 6*8 *9*
*2* *** 5**
61* *** ***
zebedee

Posts: 26
Joined: 27 March 2005

First look at box 5, and ask yourself this question: where can the number 7 go?

Then take a really good look at row 8 (and remember what you said about box 5). If you look carefully you will see a group of 3 numbers that occupies the exact same three cells... this allows you to remove all other candidates from these cells.

And that finally allows you to fill in a number in box 9.
Animator

Posts: 469
Joined: 08 April 2005

I note that the number 7 can only go in c4,r5 or c4,r6 of Box 5 but I can't see any combination of three numbers in r8 which might allow me to remove other possible numbers.

My r8 pencilmarks are as follows:

c1,r8 - 4/8/9
c2,r8 - Contains number 2
c3,r8 - 4/8/9

c4,r8 - 1/4
c5,r8 - 1/3/7/9
c6,r8 - 1/4/9

c7,r8 - Contains number 5
c8,r8 - 1/6/7/8
c9,r8 - 3/6/8

Zeb
zebedee

Posts: 26
Joined: 27 March 2005

edit: Sorry, replied then realised your pm's are not exactly the same as mine so will let Animator or someone else more advance than myself reply.
Roz

Posts: 34
Joined: 25 May 2005

Zeb..

r8c5 and r9c5 must have a pair ...so you can eliminate 2 numbers from those you've got in c5,r8.

secondly, look carefully at which cells in row 8 the numbers 3,6 and one other number can go in....
Arnie

Posts: 49
Joined: 19 May 2005

The group of numbers you should be looking for on row 8 are:
* first group: 3, 6, 7
* second group: 1, 4, 8, 9

Arnie is right that you can remove some candidates from r8c5 but if you see the groups on row 8 then you will remove exaclty the same candidates :)
Animator

Posts: 469
Joined: 08 April 2005

Arnie/Animator,

Many thanks for your kind advice. I've now solved the puzzle. I was looking for an X-wing that wasn't there and missed other, perhaps easier to spot, clues.

Zeb

zebedee

Posts: 26
Joined: 27 March 2005