Use simple logic to fill in the nine rows and nine columns with numerals 1-9. Each number can only be used once in a given row or column. Enter the correct number in every grid square to win! Sudoku has two modes: Pen and Pencil. You can pencil-in several guesses per square. Click on the hint button, located in the main menu, to see possible answers highlighted in red. You can also click on the progress button to see if you have made any mistakes. Click on the pen button, then left-click on a square and drag the cursor up and down to enter your pen answer. You can also type in the number. If you are not sure of an answer, you can select the pencil button instead. Mouse over a square and click on the number(s) you want to enter.