Can only get one number

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Can only get one number

Postby Stuck » Mon Feb 16, 2015 8:23 am

This is the London Evening Standard £50 puzzle from 10/2/15. It says it has a target time of 30 minutes. I can only get one number, a 5, in the bottom right large square. No one else I've shown it too can get past one number. Seeing the solution is no help, because that doesn't show me how it can be solved. Can anyone show me how to get, say, a second, third and fourth number? I know that it cannot be impossible, because they want readers to text in entries at £1 a time.
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Re: Can only get one number

Postby JasonLion » Mon Feb 16, 2015 2:10 pm

Consider what digits can go in R4C6. Having solved that you should be able to place a digit in block 2. The fourth move involves locked candidates, and further down the road you will need several additional more complex techniques. This puzzle is quite difficult by typical newspaper standards, but I consider it on the easy side compared to what we normally talk about here.
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Re: Can only get one number

Postby SteveG48 » Mon Feb 16, 2015 3:21 pm

Stuck, if you're not familiar with the term X-wing, you might want to check that out.
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Re: Can only get one number

Postby Leren » Mon Feb 16, 2015 8:36 pm

As Jason said, you should be able to immediately place a 2 in Row 4 Column 6 (r4c6) because it's the only number that can possibly go there.

You can then get a third number quite easily. Since r4c6 is 2, now look at Column 4. There is only 1 cell in that column that 2 can go. It's in Row 1, so r1c4 = 2.

To get a fourth number you will have to be familiar with a few other techniques to reduce the number of candidates that can go in a cell. You will have to understand at least pointing pairs and X-Wings.

Have a look at this site and study all the Basic Strategies and X-Wing Family. http://www.sudokuwiki.org/Strategy_Families

Alternatively look at this site http://hodoku.sourceforge.net/en/techniques.php and study the sections on Singles, Intersections, Hidden Subsets, Naked Subsets and X-Wing.

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Re: Can only get one number

Postby Stuck » Wed Feb 18, 2015 10:09 am

Thank you all.
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