Divide students into groups of four. Each group will receive a set of placements (1-6, depending on time). Each student will complete his/her problem on a whiteboard. After all members of the group have finished, the group will add all of their answers together. One student will write the sum of their answers in the circle on the mat. If the group is correct, they will move to the next placemat.If the group is incorrect, they will look through each other’s work to identify and fix the mistake.