The purpose of this activity is for students to add and subtract within 20. Students are encouraged to find sums and differences in as many different ways as they can. They record their thinking and then do a Gallery Walk to look at their classmates’ work. Set-up for the Gallery Walk by putting all the posters for a specific expression together. The Activity Synthesis focuses on how decomposing a number to lead to a ten can be a helpful method when subtracting within 20 (MP7).
This activity uses MLR7 Compare and Connect. Advances: representing, conversing.

• “What is the same and what is different about how you and your classmates added or subtracted?” (Some of us wrote equations. Some of us made 10 for the addition and subtraction expressions.)
• Display , , .
• “How did this student find the difference between 13 and 6?” (They broke 6 into 3 and 3. They took 3 from 13 to get to 10, and then took the other 3 away.)
• “Why is it helpful to look for ways to get to a 10 when subtracting?” (Once you are at 10, it is easy to subtract another number because we know our ten facts.)

The purpose of this activity is for students to practice adding and subtracting within 20. Students add to find the sum of two numbers, and either add or subtract to find the unknown addend when one addend and the sum are given.

• “During one round of Heads Up, Diego’s partner had a 3 on their card. Diego was told that the sum of their numbers was 12. What equations can Diego use to figure out what number is on his card?” ( or )
• “Explain which of these equations you would use to find the unknown number.” (I would use because it is really easy to count back 3. I would choose , because I prefer adding. I would add 7 to get to 10 and then 2 more.)