Variations on Advanced Sudoku Logic Puzzles (Vol 1) 
 Chapter 28: Four Medium Sudoku-15 Puzzles (numbers 91-94) 
 
-  Step-by-step instructions for solving  Puzzle 91, (87/225)   Diff: 5/9.9532
 -  Step-by-step instructions for solving  Puzzle 92, (104/225)   Diff: 5/9.9992
 -  Step-by-step instructions for solving  Puzzle 93, (109/225)   Diff: 7/999.9999
 -  Step-by-step instructions for solving  Puzzle 94, (113/225)   Diff: 8/9999.9995