Dr. X seems to be forgetting how to protect his secrets! Kid detective Jo Hammet has succeeded in getting the answers she needed from his henchmen. All you have to do is fill in the missing operation signs. Oh, wait. Turns out it wasn’t that easy after all. Martin has just tipped Jo off – can you work around Dr X’s tricks and find out the correct answers? Kids practice solving addition and subtraction problems in this printable worksheet.