This resource has 19 unique cards. Give one card to each student. The students will have to solve the equation to find the missing addend. Once they have solved their equation, they need to find their partner -- the person who solved their own equation and got the same missing addend. There is one group of three in this resource (the card that is alone on the page is the one that can be added for a group of three or not given to a student so that there are only groups of two). If a student can't find a partner, suggest that they may not have the correct answer! This activity took my 4th grade students about 15 minutes.