dailysudoku.com

[JohnInOregon]

I have a question about the 7/31/06 puzzle. I apply simple
methods and fill in 11 entries, but then get stumped. The 'Hint'
function of Draw/Play says that for row 7, column 6 (counting from
the top left) the entry has to be 9. Can anyone tell me why?

The puzzle at the point where I am stumped is as follows:
7bbbb2bbb
bb497bb12
b82bbbb4b
625b941bb
873b2b954
bbb75b62b
b3bbb?26b
29bb87435
bbb2bbbb1

'b' stands for blank and I have put a '?' where the hint
says it must be a '9'. This puzzle is rated hard, but before and
after this single entry it is easy.

Thanks for the hint explanation.
John

[David Bryant]

Hi, John! Which part of Oregon?

The short answer is that there's a naked triplet {1, 4, 5} in r7c145, so that "9" becomes the sole candidate at r7c6. That may be Greek to you, so let me explain.

-- The only values that can possibly fit at r7c6 are, apparently, {1, 5, 9}; you can see this by simply counting the possibilities.

-- Similarly, the only possibilites at r7c1 are {1, 4, 5}. At r7c4 the possibilities are also {1, 4, 5}. And at r7c5 the possibilities are {1, 4}.

-- A moment's reflection will convince you that the three values {1, 4, 5} must fit in the three cells r7c1, r7c4, & r7c5 in some order. Therefore none of these values can possibly fit anywhere else in row 7, so the only possibility at r7c6 is "9". dcb

[Rick Kent]

Is this puzzle rated "hard" or "very hard"?

This puzzle is initially rated as "Hard" but when I press the "Grade" button on the initial puzzle, it changes the difficulty rating to "very hard".

Why would that be?

- Rick.