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The purpose of this Warm-up is to re-introduce tape diagrams for inequalities, which may be useful when students interpret related quantities in word problems in a later activity. While students may notice and wonder many things about these images, these are the important discussion points:
This prompt gives students opportunities to see and make use of structure (MP7). They might apply the structure that is familiar from representing equations and recognize how the same structure can be applied to inequalities.
Arrange students in groups of 2. Display the image for all to see. Ask students to think of at least one thing they notice and at least one thing they wonder. Give students 1 minute of quiet think time, and then 1 minute to discuss with their partner the things they notice and wonder.
What do you notice? What do you wonder?
Ask students to share the things they noticed and wondered. Record and display their responses without editing or commentary. If possible, record the relevant reasoning on or near the image. Next, ask students, “Is there anything on this list that you are wondering about now?” Encourage students to observe what is on display and respectfully ask for clarification, point out contradicting information, or voice any disagreement.
If representing the tape diagram with an inequality does not come up during the conversation, ask students to discuss this idea.
In this activity, students analyze four situations and select the inequality that best represents each situation.
Students may notice and make use of structure (MP7) when reasoning about how the relationships in the situations can be represented by a specific inequality.
Tell students that their job in this activity is to read four situations carefully and decide which inequality best represents each situation. Give 5–10 minutes of quiet work time.
If needed, point out that none of the situations give the total. Students must infer what the total is based on the given inequality choices. For example, in the first situation every inequality has 3 numbers: , 5, and 25. The problem states that and 5 describe the parts, so we can infer that 25 is the total.
Choose the inequality that best matches each given situation. Explain your reasoning.
If needed, discuss which inequalities are correct. Otherwise, proceed to the next activity where students will continue working with these situations. Consider not validating which inequalities are correct at this time. When students get into groups for the next activity, they can compare their responses with the members of their groups and resolve any discrepancies at that time.
In this activity, students interpret parts of an inequality in context, term by term; for example, what quantity must represent? Then they make sense of the entire inequality by thinking about what question would be answered by the solution to the inequality. Monitor for groups that create displays that communicate their mathematical thinking clearly, contain an error that would be instructive to discuss, or organize the information in a way that is useful for all to see. At this point, there is very little scaffolding for the solving of the inequality itself.
Arrange students in groups of 2–3 and provide tools for making a visual display. Assign one situation to each group. Note that the level of difficulty increases for the situations, so this is an opportunity to differentiate by assigning more or less challenging situations to different groups.
Your teacher will assign your group one of the situations from the previous task. Create a visual display about your situation. In your display:
Explain what the solution means in terms of the situation.
Select groups to share their visual displays. Encourage students to ask questions about the mathematical thinking or design approach that went into creating the display. Here are questions for discussion, if not already mentioned by students:
Alternatively, have students do a Gallery Walk in which they leave written feedback on sticky notes for the other groups. Here is guidance for the kind of feedback students should aim to give each other:
Share with students, “Today we solved inequalities and explained what our solutions represented about the situation.”
Ask students to consider, “What if someone asked for your help with how to solve inequalities? What would you tell them? How would you describe to someone how to solve any inequality?” Ask students to either record their answer or share their thoughts with their partner. Consider creating a persistent visual display that shows the procedure, using language the class develops, along with an example.
Many real-world problems can be represented and solved by using inequalities. Writing inequalities is very similar to writing equations to represent a situation. The expressions that make up the inequalities can be thought of in much the same way as the expressions that make up equations. For inequalities, we also have to think about how expressions compare to each other—which one has a greater value, which one has a lesser value, and can they also be equal?
For example, a school fundraiser has a minimum target of \$500. Faculty have donated \$100 and there are 12 student clubs that are participating with different activities. How much money would each club need to raise if the 12 clubs shared the responsibility of meeting the goal equally? If is the amount of money that each club raises, then the solution to is the amount each club has to raise to meet the goal. It is more realistic, though, to use the inequality , since the more money raised, the more successful the fundraiser. There are many solutions because there are many different amounts of money the clubs could raise that would get them above their minimum goal of \$500.