These 99 number-crunching puzzles are sudoku PLUS! Just like the familiar sudoku that solvers love, the grids go from 1 to 9, and each number appears only once in each row, column, and box. The twist is, you need to do a little arithmetic, too—multiplying, dividing, adding, and subtracting according to the signs in the grid. It’s a fresh, challenging, and mathy take on the super-popular puzzles.