standard_description: Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts. Identify line-symmetric figures and draw lines of symmetry.
problem_activity: Narrative
The purpose of this activity is to use the standard algorithm to add multi-digit numbers, taking care to compose a new unit and record it accurately. They also analyze common errors and critique the given reasoning when composing a new unit (MP3).
Required Materials
Materials to Gather
Grid paper
Launch
Groups of 2
“Complete the first 2 problem and then talk to your partner about any patterns you notice.”
Activity
3 minutes: independent work time
2 minutes: partner discussion
Share and record responses.
If needed, use the expanded form to help students make connections between the way composing a larger unit is recorded when using the standard algorithm and what is happening in each place. In the bottom line of the example here, we see 10 in the ones place and 100 in the tens place. Both partial sums do not match the assigned values of their places.
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3–4 minutes: independent work time for the last problem.
Student Facing
Find the value of each sum.
a
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b
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c
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d
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Use the expanded form of both 8,299 and 1,111 to check the value you found for the last sum.
Each computation shown has at least one error. Find the errors and show the correct calculation.
a
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b
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c
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d
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Student Response
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Advancing Student Thinking
Students may need support identifying errors in the last problem. Consider asking: “How might subtraction be used to help identify the error?”
Activity Synthesis
Ask students to share the errors they identified in the last set of questions.
“What are some common errors when adding large numbers?”


aligns: no