Variations on Sudoku-by5 Logic Puzzles (Vol 1) 
 Chapter 19: Three Difficult Education-Xtreme Puzzles (numbers 49-51) 
 
-  Step-by-step instructions for solving  Puzzle 49, (255/369)   Diff: 11/999.9999.9992
 -  Step-by-step instructions for solving  Puzzle 50, (257/369)   Diff: 14/99.9999.9992.B472
 -  Step-by-step instructions for solving  Puzzle 51, (258/369)   Diff: 14/99.9999.9999.9673