Task Teacher Guide

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In This Task…

Students will determine which store is offering the best value for jellybeans. 

Intentionality…

The purpose of this task is to give students an opportunity to apply their understanding of ratios and rates. Students will either scale the composed unit in tandem by revealing a scale factor, or leverage the rate that exists within this composed unit. Students will build fluency finding unknown values using ratio and/or rate reasoning for the purpose of comparison. Today’s task promotes consumer awareness as students determine the best value for their money when deciding between two stores to buy jelly beans. Some of the following big ideas may emerge in this task: 

• There are two types of ratios; composed unit and multiplicative comparison;
• A composed unit is often (not always) a ratio with two distinct units; 
• A composed unit can be scaled in tandem; 
• When you divide a composed unit through partitive division, you reveal a rate; 
• Composed units can be scaled to the same quantity of one variable in order to identify the “better buy”;
• Unit rates can be used to make direct comparisons in order to identify the “better buy”.

Prerequisite unit:

If your students do not currently have a solid understanding of the implications of division on ratio and rate reasoning, consider trying Planting Flowers before moving on to this unit.

Spark

What Do You Notice? What Do You Wonder?

Show students this video:

Then, ask students:

What do you notice?

What do you wonder?

Ask students to engage in a notice and wonder protocol. ANYTHING and EVERYTHING that comes to mind is fair game. 

Here’s some of the “everything and anything” students noticed and wondered on chart paper:

• I notice a scale.
• I wonder if this is at a grocery store.
• I notice some kind of colourful candy.
• I wonder if they are jelly beans.
• I notice 3 on the scale. 
• I notice $13.50. 

Estimation: Prompt

Student prompt:

Which store is offering a better deal on jelly beans?

Make an estimate.

Have students make predictions by reasoning through their comparison of the two stores through conversation alone. 

Give students an opportunity to discuss their reasoning with a partner for about 2 minutes. 

Take a vote from students on which store will offer the best value for jelly beans. Do not have students share their justification at this point, this may rob the thinking from fellow classmates.

Sense Making

A Productive Struggle: Prompt

Show students the following screenshot and follow-up with the prompt verbally:

You have been asked to purchase 6 pounds of jelly beans for a large event with a limited budget. Which store, Bargain Bin or Deal City is offering the best value for jelly beans? Where will you be shopping for jelly beans and why? 

Use a model of your choice to convince your math community.

We will have students engage in this task without the aid of a calculator and thus we will promote the use of mathematical models as tools for thinking and representing their thinking.

During Moves

While Students Are Productively Struggling…

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Student Approach #1: Scaling up in the ratio table

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Student Approach #2: Scaling down in the ratio table

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Student Approach #3: Using partitive division to reveal a rate

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Next Moves

Consolidation: Making Connections

The comparison of the quantities of pounds to dollars in this scenario is a specific type of ratio called a composed unit where one can consider the two quantities in the ratio as a single unit. For example, when we consider the 3 pounds and $13.50, we can view these two quantities together as one unit (composed of two unique units) that can increase and decrease in tandem (together).  

Some students likely used the composed unit to scale the ratio up to 6 pounds or down to 1 pound in order to compare. Some students may have also scaled up to a common multiple of 3 and 4 such as 12, and then possibly divided by two. 

We are going to call this strategy ratio reasoning.

Scenario 1:

Scenario 2:

Scenario 3:

A second strategy that may have been used is revealing a rate through partitive division. When we take the two quantities within a composed unit and divide through partitive division, a rate is revealed. A single quantity with a compound unit (dollar/pound or pound/dollar).

We are going to call this strategy rate reasoning.

Reveal

Show students different variations of the reveal videos below.

Here is a screenshot of the final frame of reveal video:

Reflect

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

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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.