Index cards with a number 0-9 on each, and several plus, minus, division, multiplication signs. Each student gets a card with a number on it. On command, teacher calls out a sum of a math problem. Students find others to figure with their number in that math problem. Plus, minus, division and multiplication signs are in front of the room, and students can get the ones they need to answer the problem.
Students arrange themselves in order to form the correct problem.
Teacher chooses the problem that was the most difficult to arrange, or the one that uses the most students. After a few rounds, students can exchange their numbers. Add other variations to change the game.