Task Teacher Guide

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Students will explore subtraction in a context by taking numbers away from ten. A connection can be made to the combinations that make ten. 

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In this task, students will explore subtracting from teen numbers to make a difference of 10. This skill is another step towards the efficient subtraction strategy of Down and Under Ten. This strategy uses 10 as a bridge so the lesson focuses on a teen number as the minuend and the corresponding subtrahend that would be needed to make a difference of 10. (e.g. 14 – 4 = 10) Some of the big ideas revealed in today’s lesson include:  

• Understanding hierarchical inclusion allows for flexible composing and decomposing of numbers
• Numbers can be decomposed by separating a whole into two or more parts
• Subtraction names the missing part in terms of the whole
• Different subtraction situations will elicit different strategies 
• Number relationships provide the foundation for strategies to help students remember basic facts
• Addition and subtraction are related in that addition names the parts in the whole and subtraction uses the whole to find a missing part. 
• Subtraction can be used in either take away, comparison, or missing addend situations.
• Models can be used to connect concrete to abstract 

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Spark

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Show students the following video:

Then, ask students:

What do you notice?
What do you wonder?

Give students 60 seconds (or more) to do a rapid write on a piece of paper.

Then, ask students to share with their neighbours for another 60 seconds.

Finally, allow students to share with the entire group.

Some of the noticing and wondering that came up in a class recently included:

• I notice a pear tree. 
• I notice there are pears in a basket. 
• I notice that some of the pears are on the ground.
• I wonder if we can eat the pears
• I wonder if the other basket is empty
• I wonder how many pears are in the basket.

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Next, share the following visual prompt briefly and ask the following question:

How many pears are in the basket?

Have students make estimates first by thinking about an amount of pears that they believe will be too low, followed by an amount that they think will be too high.

Challenge students to be risky with their low/high estimates.

Then, have them pick their best estimate and share with their neighbours before sharing and recording on the chalk/whiteboard or chart paper as a class.

Ask students what information they might need in order to figure out the answer.

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[accordion-item title=”Estimation: Reveal”]

Share the following video revealing how many pears are in the basket.  

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Sense Making

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[accordion-item title=”Crafting A Productive Struggle: Prompt”]

Since you have already taken some time to set the context for this problem and student curiosity is already sparked, we have them in a perfect spot to help push their thinking further and fuel sense making.

If the frame picks 6 pears, How many pears will still be on the tree? 

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During Moves

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[accordion-item title=”Student Approach #1: Using a Pictorial Representation and Counting”]

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[accordion-item title=”Student Approach #2: Counting Back using Fingers”]

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[accordion-item title=”Student Approach #3: Known Addition Fact”]

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Next Moves

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[accordion-item title=”Consolidation: Making Connections”]

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Show students the following reveal video:

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Provide students an opportunity to reflect on their learning by offering these consolidation prompts to be completed independently.

Consolidation Prompt #1:

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Consolidation Prompt #2:

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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

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.