Task Teacher Guide
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In This Task…
Students will explore the final subtraction structure: missing addend.
Intentionality…
The purpose of the Day 5 activities is to reinforce the part-whole model from day 4 and to explore a new subtraction structure; missing addend. Students will engage in a math talk, investigate a new task and independently complete purposeful practice. Today’s learning serves to develop a deeper understanding of the following big ideas.
- Part-whole relations: Relationships between addition & subtraction.
- One-to-one correspondence.
- Measured and unmeasured comparison can be used to describe the relationship between two quantities
- One structure of subtraction is “missing subtrahend”.
- One structure of subtraction is “missing addend”.
Math Talk
Related String of Problems
Through the following math talk, students will be tasked with solving for unknown subtrahends. Students might consider using a concrete, pictorial or abstract part-whole model to make sense of the following number sentences. Once students make sense of the information, it is likely that many students will use a counting on strategy (reinforcing the relationship between addition and subtraction). Consider creating a context to help students visualize what is happening.
9 –
= 5
11 –
= 8
16 –
= 12
22 –
=15
29 –
= 18
Spark
Building On The Context Through Storytelling
Remind students of the context developed on Day 4, where there were gummy worms missing from the jar. For today’s task, you might also consider bringing back your jar of gummy worms and explaining today’s context orally.
As you know, I had a 17 gummy worms left in the jar yesterday after 8 were eaten. I went to the store last night and I bought more gummy worms, but now, there are 32 gummy worms in the jar. How many gummy worms did I buy last night?
Sense Making
Crafting A Productive Struggle: Prompt
Share the prompt with students:
If there were 14 gummy worms yesterday, and now there are 30, how many more did I buy?
Facilitator Notes
In this task, students will have an opportunity to reason through a subtraction scenario. This particular problem is an example of the “missing addend” subtraction structure. This task will allow students to apply a variety of strategies and models, while developing a deeper understanding of big ideas, specifically the following;
- Part-whole relations: Relationships between addition & subtraction.
- One structure of subtraction is “missing addend”.
During Moves
While Students Are Productively Struggling…
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Student Approach #1: Concrete & Part Whole Model One-to-One
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Student Approach #2: Concrete & Part Whole Model Count 3 Times
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Student Approach #3: Number Path & Skip Counting By 2s
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Student Approach #4: Number Line & Friendly Numbers
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I know that you had 14 yesterday. So I put the 14 here on my number line. And I know that today you have 30, so I just have to figure out how many I need to add to 16 to get 30. I started by adding 6, that gets me to 20. Then I added 10 more, because I know 20 + 10 + 30.
Strategy:
This student used a number line and started with the known part (14 gummy worms). They counted on by taking leaps to friendly numbers on the number line (a leap of 6 and a leap of 10). In this model, you can see the two parts nested in the whole.
Next Moves
Consolidation
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Purposeful Practice
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We suggest collecting this reflection as an additional opportunity to engage in the formative assessment process to inform next steps for individual students as well as how the whole class will proceed.
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Resources and Downloads
Lesson Tip Sheet
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Explore The Entire Unit of Study
This Make Math Moments Task was designed to spark curiosity for a multi-day unit of study with built in purposeful practice, and extensions to elicit and emerge mathematical models and strategies.
Click the links at the top of this task to head to the other related lessons created for this unit of study.
How many?
9 –
= 5
…
11 –
= 8
…
16 –
= 12
…
22 –
= 15
…
29 –
= 18
Prompt:
If there were 14 gummy worms yesterday, and now there are 30, how many more did I buy?
1. Cookies: Prompt
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1. Cookies: Image
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2. Raking Leaves: Prompt
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2. Raking Leaves: Image
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3. Ducks
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4. Write…
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Download Editable/Printable Handout
Become a member to access purposeful practice to display via your projector/TV, download the PDF to upload to your LMS and/or print for students to have a physical copy