Students will explore a third subtraction structure: missing subtrahend.

The purpose of the Day 4 activities is to reinforce key concepts from Day 3 and to explore a new subtraction structure; missing subtrahend. 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 “removal”.
• One structure of subtraction is comparison (or difference).
• One structure of subtraction is “missing subtrahend”.

Through the following string or related problems, students might be encouraged to use a variety of strategies, depending on the numbers in the subtraction sentence. When the numbers are close together, students are likely to see this subtraction as “difference” and they may use a strategy such as “counting on”. When the subtrahend (the second number in the sentence) is significantly smaller the minuend (the first number), students may view this subtraction as “take away” or separate and are more likely to count back by ones and take jumps to friendly numbers.  Consider modelling student thinking on a concrete number line or number path. Be sure to highlight the two different subtraction structures.

10 – 1

10 – 9

15 – 12

15 – 3

17 – 4

17 – 13

Remind students of the context developed on Day 1 and 3. 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 jar that contained 25 gummy worms. When I came back this morning, there were only 14 gummy worms left in the jar. At some point last night, someone must’ve come in and helped themselves to some gummy worms. I am wondering how many they ate so that I can go to the store and replace them. Can you help me figure it out?

Share the prompt formally with students:

There were 25 gummy worms in the jar. Now there are only 14 left. How many gummy worms were eaten?

In this task, students will have an opportunity to reason through a subtraction scenario. This particular problem is an example of the “missing subtrahend” 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 subtrahend”.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.

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.

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

JOIN TO DOWNLOAD