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Theme: Surrounded

Author/Opus: This is the 557th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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Theme: Sunshine

Author/Opus: This is the 556th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Backslashes

Author/Opus: This is the 555th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: DUET

Author/Opus: This is the 554th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Two Sides

Author/Opus: This is the 553rd puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Either/Or

Author/Opus: This is the 552nd puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: The Eight Tees

Author/Opus: This is the 551st puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Open Middle

Author/Opus: This is the 550th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Stripes

Author/Opus: This is the 549th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Fill each cell with an X or O so that (A) no vertical or horizontal group of three adjacent cells contains the same symbol in all cells (i.e., no XXX or OOO) and (B) each row and column contains an equal number of each symbol. Cells separated by an equals sign (=) must contain the same symbol. Cells separated by a cross (×) must contain different symbols.

Solution: PDF and selected animation.

Note: Follow this link for other Number Placement puzzles.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Thirteen Days of Tango Discussion post on the GMPuzzles Discord.

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or solve online (using our beta test of Penpa-Edit tools)

Theme: Clued Descending a Staircase

Author/Opus: This is the 548th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Sudoku rules.

Time Standards (highlight to view): Grandmaster = 6:15, Master = 9:15, Expert = 18:30

Solution: PDF and solving animation.

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More Sudoku including variations can be found in these books in our e-store. Also, visit this page to purchase all of the puzzles from the 16th World Sudoku Championship including classic Sudoku.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our The Twelve Days of Sudoku Discussion post on the GMPuzzles Discord.

Note 3: Please check lesson notes from Dr. Sudoku on Google Docs.

Note 4: Thanks to Tyler Hinman for suggesting this playful title long ago for another puzzle (unused then but adopted here).