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Sat 28-May-2005 very hard

 
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Beginner
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PostPosted: Wed Aug 17, 2005 8:07 pm    Post subject: Sat 28-May-2005 very hard Reply with quote
After having entered all numbers I could find for this Sudoku I ended up with:
Code:
-3- 2-- 781
--8 *-- 3-4
-74 -3- 96-
--- 18- 6-7
-17 6-9 -38
8-- 375 149
-41 -6- 89-
7-- --- 41-
98- 413 -7-

where * marks the spot where I have no entry but the hint given by the drawer is a 7. Can somebody help me understand this hint, it's logic escapes me completely.
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Guest
PostPosted: Wed Aug 17, 2005 10:15 pm    Post subject: Reply with quote
r2c2 can be 2, 5, 6, 9
But in column 1, 6 can only be in row 1 and row 2, which means 6 in r2c2 can be eliminated, leaving 2, 5, 9

The * can be 5, 7, 9
r2c5 can be 2, 5, 9
r2c8 can be 2, 5

r2c2, r2c5, r2c8 only has numbers 2, 5, 9. Which means those numbers will only be available in those 3 spaces. So we can eliminate these numbers from the other columns in row 2.

So * can ONLY be 7 after eliminating 5 and 9.
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Beginner
Guest
PostPosted: Thu Aug 18, 2005 9:01 pm    Post subject: Reply with quote
Anonymous wrote:
r2c2 can be 2, 5, 6, 9
But in column 1, 6 can only be in row 1 and row 2, which means 6 in r2c2 can be eliminated, leaving 2, 5, 9
Agreed.
Anonymous wrote:
The * can be 5, 7, 9
r2c5 can be 2, 5, 9
r2c8 can be 2, 5

r2c2, r2c5, r2c8 only has numbers 2, 5, 9. Which means those numbers will only be available in those 3 spaces. So we can eliminate these numbers from the other columns in row 2.

So * can ONLY be 7 after eliminating 5 and 9.

Now I am lost. How can r2c5 contain a possible 2 when there is a 2 in r1c4? Why is there no 2 or 5 possible in r2c1?
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Guest
PostPosted: Thu Aug 18, 2005 9:31 pm    Post subject: Reply with quote
Beginner wrote:
Now I am lost. How can r2c5 contain a possible 2 when there is a 2 in r1c4? Why is there no 2 or 5 possible in r2c1?


Okay, I mistyped it when I was typing from my solution. r2c5 can only be 5,9.

r2c1 CAN be 1,2,5,6.
r2c2 can only be 2,5,9
r2c5 can only be 5,9
r2c8 can only be 2,5

If you noticed, in row 2, 3 cells contain combination of only THREE numbers: 2, 5 and 9. No other numbers are contained in these three cells. Then that means these 3 cells will eliminate 2,5,9 from OTHER cells in row 2. So after eliminating 2,5,9 from row 2, we get

r2c1 can only be 1,6 (2 and 5 eliminated)
* can only be 7 (5 and 9 eliminated)
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Beginner
Guest
PostPosted: Fri Aug 19, 2005 7:15 am    Post subject: Reply with quote
Thanks, now I understand! Wink
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