Variations on Sudoku-by5 Logic Puzzles (Vol 1) 
 Chapter 11: Three Medium Sudoku-Xtreme Puzzles (numbers 25-27) 
 
-  Step-by-step instructions for solving  Puzzle 25, (225/369)   Diff: 7/999.9988
 -  Step-by-step instructions for solving  Puzzle 26, (228/369)   Diff: 7/999.9992
 -  Step-by-step instructions for solving  Puzzle 27, (230/369)   Diff: 7/999.9993