Lesson 4

The purpose of this warm-up is to elicit students’ understanding of line plots, which will be useful when students create and analyze line plots in a later activity. While students may notice and wonder many things about the measurement data, the characteristics of the line plot are the important discussion points.

• 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.

• “How is the line plot the same as the table? How is it different?” (They both represent the lengths of patients’ feet. They both show the same measurements. The table helps you see the length of each patient’s foot. The line plot helps you see the measurements together, but doesn’t show you which patient had which length.)
• As needed, revisit features of a line plot (scale, meaning of each X, titles).

The purpose of this activity is for students to measure the length of objects (pencils) to the nearest centimeter and record their data in a table. Students add and subtract to answer questions about the data in the table and share strategies for how they find sums and differences. The numbers in the chart were chosen to invite students to look for ways to use methods based on the properties of operations and using known sums within 20 to find the total lengths.

• Each students needs an unsharpened pencil.
• The activity works best if it is likely that students will have a range of pencil lengths between and among groups. If necessary, sharpen pencils to different lengths and distribute them randomly to students.

• Groups of 3–4
• Give each student an unsharpened pencil and a centimeter ruler.
• “Without measuring it, estimate the length of a brand new pencil.”
• 30 seconds: quiet think time
• Share responses.
• “Measure the pencil to the nearest centimeter.” (18 cm)
• 1 minute: group work time
• Share responses.

• Display the table.
• “The table shows the length of pencils from 4 different student groups.”
• “Find the length of your own pencil and share it with your group. Record your group’s measurements in the table.”
• 4 minutes: group work time
• “Use the table to find the total length of each group’s pencils.”
• 4 minutes: independent work time
• Monitor for students who:
  • look for ways to make sums by making 10 or finding easier sums

• “How did you find the total length of group _____’s pencils?”
• “Which lengths did you add first? Why?”
• “Can you think of another way to find the sum?”

• Invite previously identified students to share strategies for how they found the total lengths.
• Record equations to emphasize how students rearranged or decomposed addends to make 10 or find sums.

The purpose of this activity is for students to plot their measurement data and to use the data to answer questions (MP2). In the activity synthesis, students share the methods they use to add or subtract within 20 and discuss different ways that they can use the data in a line plot.

• Groups of 2

• “Use the table of measurements to create a line plot. When you and your partner are finished, compare your plots and work together to resolve any differences.”
• 4 minutes: independent work time
• 2 minutes: partner discussion
• “Work together to answer the questions.”
• 3 minutes: partner work time

• Invite 1–2 students to share methods for how they found the difference between the longest and shortest pencil or the difference between the shortest pencil and an unsharpened pencil. Consider selecting strategies based on making 10 and using known facts.
• “What other questions could we use the line plot to answer?” (How many people had a pencil that was _____ cm long? How many more students had a pencil that was _____ cm long than students who had a pencil that was _____ cm long?)
• Display a completed table from the first activity and a line plot from the second activity.
• “What questions are easier to answer with the line plot? Explain.“