Number enigmas

the long version

"This compilation is for those who want to maximize their mental arithmetic skills and sharpen their logical ́intuition.́ No matter what your level of ability, a carefully graded series of challenges ensures that this book has plenty for everyone. Time limits further add to the fun. Generally, logic puzzles are based on words and ideas, but there is an amazing variety of fascinating number puzzles, too. Indeed, numbers themselves are puzzles: There are twenty-six letters and only ten digits, yet the variety of words is finite while numbers are infinite."--Page [4] of cover.