The purpose of this activity is for students to measure the length of objects (pencils) to the nearest centimeter and to 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 known sums within 20 to find the total lengths.

• “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 used to add or subtract within 20 and discuss different ways that they can use the data in a line plot.

• 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.“