The purpose of this activity is for students to match story problems to equations with a symbol for the unknown. This matching task gives students opportunities to analyze story problems and equations closely and to make connections (MP2). Equations that match the Add To, Result Unknown; Take From, Result Unknown; and Put Together/Take Apart, Total Unknown problems are written to match the actions or the order the quantities are presented in the story problem.

The Put Together/Take Apart, Addend Unknown problem (Problem C) can be represented with more than one equation, which prompts students to discuss the relationship between addition and subtraction (MP7) in the Synthesis.

• “Which equation matches Problem C? How do you know?” (. 9 represents how many students were at the slide in the beginning. 6 represents how many students leave, so that is . The box represents how many are left, which is the answer to the problem.)
• Repeat for Problem D.
• Display equation Card K and Card N.
• "What do you notice about these equations?" (One is addition and one is subtraction. They both have a total of 9 and one part is 3. The other part is the unknown. They both match Problem D.)
• As needed, reread Problem D.
• “How does each of these equations match the story problem?” (There are 9 kids playing ball altogether and 5 kids are on the red team. The box is how many are on the blue team. You could think of adding more to 5 to make 9 or you could take out the red team from the total. The number of kids on the blue team would be what is left.)

The purpose of this activity is for students to interpret two different equations with a symbol for the unknown in relation to a story problem. Students are presented with a Put Together/Take Apart, Addend Unknown story problem and two equations that match it, which allows students to further explore the relationship between addition and subtraction and their understanding of subtraction as an unknown addend problem. When students explain how each equation matches the story problem and make connections between the equations, they reason abstractly and quantitatively (MP2).

• Invite previously identified students to share.
• “How do the equations relate to each other?” (They use the same numbers. The total is 9 and one part 3. The answer that goes in the box will be the same.)
• “This problem is about parts and a total. You could think about putting the part you know and the part you don’t know together like Clare did or you could think about removing one part from the total, like Jada did.”
• “How does this show we can think about subtraction as finding the value of an unknown addend?” (If you take away 3 from 9 you will find the other part. If you think about how many to add to 3, you will find the unknown part too. They have the same parts and the same total.)