The purpose of this activity is to play the same game from the previous lesson, with a focus on using the ten in the teen number to help find the difference. This time, all students use the double 10-frame to represent the teen number to encourage students to use a ten to help them subtract.

Students may start by taking away the ones from the teen number and then take additional ones from the 10-frame to determine the answer. Students may also use a different method and take away the single digit number from the full 10-frame, then count the remaining counters across both 10-frames. Or, students may count on from the one-digit number to the teen number. In each case, students write an equation to show the difference. Students may write subtraction equations or unknown addend equations.

• Invite previously identified students to share.
• “How is the game today different from yesterday?” (Yesterday we could solve any way we want, today we used 10-frames to build numbers and take away.)
• “Did the double 10-frames help? Why?” (They helped me see how I could use 10 to take away easier.)

The purpose of this activity is for students to analyze different take away methods used to find the difference between two numbers. During the Launch, students discuss the two different methods to subtract. Then they solve two problems using one of the methods they discussed. Given the first step toward a calculation, students make sense of and then complete the calculation (MP3).

During the Activity Synthesis, the teacher records equations to match the method shared. It is important that each step is written as its own equation. For example, when solving , the teacher records:

• Invite previously identified students to share.
• As each student shares, ask them to explain why they chose their method.
• “Did anyone solve it in a different way? Why?”