Calcudoku puzzles are a combination of arithmetic and logic type puzzles. Each calcudoku grid has blocks surrounded by bold lines. Each block has a math problem to solve based on arithmetic operations: addition, subtraction, multiplication or division. Numbers are placed in the blocks so that they occur only once in each row and once in each column. Similar to Sudoku. However, within each block, numbers can occur more than once. Remember: follow Sudoku puzzle rules for rows and columns.