Dan Croker has two obsessions - Sudoku and frogs. So he just had to combine his loves and make the Famous Frog Sudoku books. This Famous Frog Extra Hard Series Book contains 600 extra hard puzzles. There are 4 puzzles per page and a fun and colorful cover that is sure to brighten your day. Solutions are given at the end of the book. More Famous Frog Sudoku series - Beach Bum Series, Bathroom Sudoku, Hard Series, Brain Yoga, Sharper Pencil Series, Giant Series, Take a Break and The Travel Series.