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July 16

 
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Golfgal



Joined: 31 Jul 2006
Posts: 7

PostPosted: Mon Jul 31, 2006 2:58 pm    Post subject: July 16 Reply with quote

Have been working on this & can not seem to get it......any help greatly appreciated:

x79 8xx 5x2
x2x xx7 xx8
816 253 479

x92 x1x 84x
x8x xxx x2x
x3x x82 9xx

761 539 284
253 4x8 x9x
948 x2x 35x

The hint is 5 in R5C3

Haven't seen any discussion on this previously so must be missing something basic.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Mon Jul 31, 2006 4:16 pm    Post subject: X-Wing on the "7"s Reply with quote

Hi, golfgal!

This puzzle is pretty tough. You need the advanced technique "X-Wing" to make progress from here.

-- The apparent candidate list at r5c3 is {4, 5, 7}.

-- You can rule out a "4" because the "4" in the middle center 3x3 box must lie in row 5 (that is, either at r5c5, or at r5c6).

-- Now concentrate on columns 5 & 7. The only possible spot for a "7" in column 5 is at r5c5 or at r8c5 (because of the "7" in the top center 3x3 box). The only possible spot for a "7" in column 7 is at r5c7 or r8c7 (because of the "7" in the top right 3x3 box).

This completes the "X-Wing" formation -- there's either a "7" at r5c5, or at r5c7, and the "7" can't possibly fit at r5c3, leaving "5" as the sole candidate in that cell. dcb
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keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Mon Jul 31, 2006 4:20 pm    Post subject: Reply with quote

Code:
+-------------------+-------------------+-------------------+
| 34    7     9     | 8     46    146   | 5     136   2     |
| 345   2     45    | 169   469   7     | 16    136   8     |
| 8     1     6     | 2     5     3     | 4     7     9     |
+-------------------+-------------------+-------------------+
| 56    9     2     | 367   1     56    | 8     4     3567  |
| 1456  8     457   | 3679  4679  456   | 167   2     13567 |
| 1456  3     457   | 67    8     2     | 9     16    1567  |
+-------------------+-------------------+-------------------+
| 7     6     1     | 5     3     9     | 2     8     4     |
| 2     5     3     | 4     67    8     | 167   9     167   |
| 9     4     8     | 167   2     16    | 3     5     167   |
+-------------------+-------------------+-------------------+


The <4> in R6 is in B4. That takes out the <4>'s in R5B4. Then there is an X-wing on <7> in C57 which removes the <7> from R5C3, which must then be <5>.

Keith
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Golfgal



Joined: 31 Jul 2006
Posts: 7

PostPosted: Mon Jul 31, 2006 4:35 pm    Post subject: Reply with quote

Thank you!

Worked on it so long that I couldn't see forest for the trees!
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Marty R.



Joined: 12 Feb 2006
Posts: 5178
Location: Rochester, NY, USA

PostPosted: Mon Jul 31, 2006 9:17 pm    Post subject: Reply with quote

Quote:
Worked on it so long that I couldn't see forest for the trees!


You're hardly alone in that department!! Exclamation
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