This activity requires students to work in groups of 4. You will pass out the first set of problems to each group. Each student in the group will choose one problem to complete. After all 4 students have completed their problems, they will add their answers together and check to see if their sum matches the sum that they are supposed to get. If they do, you can give them the second set of problems. The problems progressively get more challenging, eventually leading to fractions and decimals. Not all groups will get through all problems, which allows you to challenge groups who are ready. Answer key is included!