Interactive Word Problems Addition & Subtraction within 20 Summer Edition (1.OA.1) Google SlidesPerfect for distance learning or an interactive center in your classroom! Students manipulate the digital pieces on the side as math tools. This set contains 24 slides. The word problem types are add to result unknown, add to change unknown, add to start unknown, take away result unknown, take away change unknown, take away start unknown, part-part-whole unknown, both parts unknown, part unknown,