Book excerpt: Dozens of compelling and addictive mathematical puzzles twillchallenge your mental arithmetic and powers of deductive reasoning. Tetonor rules: each number in the main grid can be formed by adding or multiplying a pair of numbers in the strip below the grid. Each pair of numbers should be used twice: once as part of an addition and once as part of a multiplication. For example, a 10 and 24 in the main grid may be solved by the sums, 4 + 6 and 4 x 6, respectively. Enter each sum in the boxes below its answer. Any blanks in the strip must be deduced, bearing in mind the numbers are listed in ascending order. 60 Easy, 80 Medium and 60 Difficult puzzles included.