This is a pack of 13 activity sheets with answer keys focused on helping students develop a deeper understanding of addition as well as practice applying their knowledge of addition. Students will be engaged in critical thinking, mental math and estimation. Their are 13 sheets and each sheet has an answer key. The activity sheets are designed for use with 3rd and 4th grade age students but could be appropriate for younger or alder students depending on their math development. These are excellent activities for learning centers, independent practice or to stimulate rich whole group math discussions.