Students will explore a second subtraction structure: difference (or comparison).

The purpose of the Day 3 activities is to reinforce key concepts from Day 1 and to explore a new subtraction structure. 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.

• Relationships between addition & subtraction.
• One-to-one correspondence.
• One structure of subtraction is “removal”.
• Measured and unmeasured comparison can be used to describe the relationship between two quantities.
• One structure of subtraction is comparison (or difference).

Through the following string or related problems, students might be encouraged to use the “taking jumps of ten” strategy, while others might begin exploring “counting on”. Some students might see the opportunity to use the strategy “one more, one less” when the subtrahend is one larger than the previous problem.

Consider recording student strategies on a concrete number line or number path. Two different structures of subtraction (separating and comparison) may emerge during this string depending on how students communicate their thinking.

13 – 10

13 – 9

13 – 11

18 – 10

18 – 11

18 – 13

Remind students of the context developed on Day 1.

For today’s task, you might consider bringing in two jars of gummy worms, or explaining the situation orally.

As you know, I have a jar that contains 25 gummy worms. When I went home last night, I saw a second jar on the counter…

[At this point, you might consider displaying both jars and proceed to ask the question]

…which jar do you think has more gummy worms?

Give students an opportunity to turn and talk and then ask a few students to share out. Encourage students to defend their answer. This conversation will lead students to the big idea of using unmeasured comparison to describe the relationship between two quantities.

Tell students that you want to be more precise, you want to know with certainty which jar has more gummy worms and to be more exact, how many more.

Consider counting the number of gummy worms in each jar together, and then sending students off to determine how many more gummy worms are in the jar with the greater quantity.

Then you can share one of the following prompt options for your students:

Prompt Option #1:

There are 25 gummy worms in the first jar and 19 gummy worms in the second jar. How many more gummy worms are in the jar with the greater quantity?

Or…

Prompt Option #2:

There are 25 gummy worms in the first jar and 19 gummy worms in the second jar. How many less gummy worms are in the jar with the smaller quantity?

In this task, students will have an opportunity to reason through a subtraction scenario. This particular problem is an example of the “comparison” subtraction structure, also referred to as “difference”. This task will allow students to apply a variety of strategies and models, while developing a deeper understanding of big ideas, specifically the following:

• Measured and unmeasured comparison can be used to describe the relationship between two quantities.
• One structure of subtraction is comparison (or difference).

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