Lesson 12

The purpose of this warm-up is for students to think mathematically about a context they will be working with in the next activity. Students may generate a variety of mathematical questions related to the story problem types they solved in previous lessons. This warm-up prompts students to make sense of a problem before solving it by familiarizing themselves with a context and the mathematics that might be involved (MP1).

• Groups of 2
• Display the image.
• “What do you notice? What do you wonder?”
• 1 minute: quiet think time

• “Discuss your thinking with your partner.”
• 1 minute: partner discussion
• Share and record responses. 

• "What math questions can you ask about this picture?"
• "We are going to work on lots of story problems about school supplies."

The purpose of this activity is for students to solve a Compare, Difference Unknown story problem using modified language. Students begin the activity by looking at the problem displayed, rather than in their books. They identify the important quantities before working on the problem, giving them an entry point for addressing the question, phrased negatively, of how many students will not have a pencil (MP1). When students open their books and work on the problem, they have access to connecting cubes or two-color counters. In the lesson synthesis, students connect equations to different ways of solving the problem.

This activity uses MLR6 Three Reads. Advances: reading, listening, representing.

• Groups of 2
• Give students access to connecting cubes or two-color counters.

MLR6 Three Reads

• Display only the problem stem, without revealing the question(s). 
• “We are going to read this problem three times.”
• 1st Read: “There are 10 students at the table. There are 6 pencils.”
• “What is this story about?”
• 1 minute: partner discussion
• Listen for and clarify any questions about the context.
• 2nd Read: “There are 10 students at the table. There are 6 pencils.”
• “What are all the things we can count in this story?” (the number of students, the number of pencils)
• 30 seconds: quiet think time
• 1 minutes: partner discussion 
• Share and record all quantities.
• Reveal the question(s).
• 3rd Read: Read the entire problem, including question(s) aloud.
• “What are different ways we can solve this problem?” (I can use red connecting cubes for the students and blue for the pencils. I can draw circles for the students and lines for the pencils.)
• 30 seconds: quiet think time
• 1 minute: partner discussion
• "Solve the problem."
• 3 minutes: independent work time
• “Share your thinking with your partner.”
• 2 minutes: partner discussion
• Monitor for a student who represents counting up from 6 to 10 and one who represents subtracting 6 from 10.

• Display previously identified student work.
• “How did they solve the problem?”
• Write an equation to match each method of solving.

The purpose of this activity is for students to represent and solve Compare, Difference Unknown story problems. Students may use one of the following methods to find the difference or may come up with their own method.

In the activity synthesis, students consider methods related to counting up and counting back.

• Groups of 2
• Give students access to connecting cubes or two-color counters.

• “You will solve more story problems about school supplies. Show your thinking using drawings, numbers, or words. Write an equation for each story problem.”
• 6 minutes: independent work time
• 3 minutes: partner discussion
• Monitor for a student who counted up and one who counted back for the problem about folders.

• Invite previously identified students to share.
• “How is their work the same? How is it different?” (They both use 2, 7 and 9. One uses addition and one uses subtraction. The answer is in a different place in each equation.)
• “Where is the answer to the question in each representation?” (When they added the answer was in the middle. When they subtracted it was at the end.)
• Add a box around the answer in each equation.