1000 Hard Sudoku Puzzles To Improve Your IQ (IQ BOOST PUZZLES) (Volume 10)

SCIENTIFICALLY PROVEN THAT REGULAR SUDOKU PUZZLE SOLVING IMPROVES IQ AND KEEPS BRAIN IN TOP SHAPE. THIS BOOK HAS 1000 9x9 HARD SUDOKU PUZZLES WITH SOLUTIONS. COMPUTER CAN SOLVE HARD SUDOKU PUZZLES IN 4-8 SECONDS. EACH PUZZLE WAS CHECKED FOR A SINGLE SOLUTION. IQ CAN BE INCREASED BY SOLVING 3-5 SUDOKU PUZZLES WEEKLY.