Each card has a problem and the answer to another problem is in the box in the lower right corner. Post cards around the room (I like to put them on bright colored card stock so they are easily found. Students can start on any problem they want. Once they complete the problem, they go find their answer on the bottom of another card. If they don't find their answer, they did something wrong. If they get all answers right, they will know because they will have completed all problems and the last problem will lead them back to the first. Great activity for students to self check.