Variations on Advanced Sudoku Logic Puzzles (Vol 1) 
 Chapter 36: Four Challenging Sudoku-15up Puzzles (numbers 119-122) 
 
-  Step-by-step instructions for solving  Puzzle 119, (133/225)   Diff: 15/966.5776.9999.9982
 -  Step-by-step instructions for solving  Puzzle 120, (124/225)   Diff: 16/9855.7988.7689.7952
 -  Step-by-step instructions for solving  Puzzle 121, (125/225)   Diff: 16/9555.6986.5548.9992
 -  Step-by-step instructions for solving  Puzzle 122, (118/225)   Diff: 20/9997.2473.2223.5673.5832