Besides developing an understanding of part-part whole relationships, these cards help students learn about the inverse relationship between addition and subtraction and develop a rudimentary understanding about the connection between subtraction and adding the opposite. This activity is meant to help students develop an efficient strategy for computation. This computational fluency is a precursor to students developing mental fluency. This activity is aligned to the following Common Core State Standard domain: The Number System. These cards may be used with partners or as a teacher-led activity with groups of students.