Have students search the room for the different QR codes. A picture will pop up on their screen of and addition/subtraction problem being represented by shapes. Students then write that number sentence next to the shape they see. I suggest printing QR codes on card stock and laminating for durability. Put up only one set at a time to avoid confusion, or print the answer sheet double sided and see if they can determine if it is an addition or subtraction problem for themselves! I have also printed and laminated the answer sheets for a reusable center.