options: Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.

Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.
problem_activity: Activity
The purpose of this activity is for students to interact with contexts in which the direction of inequality is the opposite of what they might expect if they try to solve like they would with an equation. For example, in the second problem, the original inequality is
\(9(7-x) \leq 36\)
, but the solution to the inequality is
\(x \geq 3\)
.
Some students might solve the associated equation and then test values
of
\(x\)
to determine the direction of inequality. That method will be introduced in more generality in the next lesson. This activity emphasizes thinking about the context in deciding the direction of inequality.
Launch
Keep students in the same groups. Give 5–10 minutes of quiet work time and partner discussion followed by a whole-class discussion.
Student Facing
Kiran has
$
100 saved in a bank account. (The account doesn’t earn interest.) He asked Clare to help him figure out how much he could take out each month if he needs to have at least
$
25 in the account a year from now.
Clare wrote the inequality
\(\text-12x + 100 \geq 25\)
, where
\(x\)
represents the amount Kiran takes out each month. What does
\(\text-12x\)
represent?
Find some values of
\(x\)
that would work for Kiran.
We could express
all
the values that would work using either
\(x \leq \text{__ or } x \geq \text{__}\)
. Which one should we use?
Write the answer to Kiran’s question using mathematical notation.
A teacher wants to buy 9 boxes of granola bars for a school trip. Each box usually costs
$
7, but many grocery stores are having a sale on granola bars this week. Different stores are selling boxes of granola bars at different discounts.
If
\(x\)
represents the dollar amount of the discount, then the amount the teacher will pay can be expressed as
\(9(7-x)\)
. In this expression, what does the quantity
\(7-x\)
represent?
The teacher has
$
36 to spend on the granola bars. The equation
\(9(7-x)=36\)
represents a situation where she spends all
$
36. Solve this equation.
What does the solution mean in this situation?
The teacher does not have to spend all
$
36. Write an inequality relating 36 and
\(9(7-x)\)
representing this situation.
The solution to this inequality must either look like
\(x \geq 3\ \text{or } x \leq 3\)
. Which do you think it is? Explain your reasoning.
Student Response
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for free access to Student Response.
Student Facing
Are you ready for more?
Jada and Diego baked a large batch of cookies.
They selected
\(\frac14\)
of the cookies to give to their teachers.
Next, they threw away one burnt cookie.
They delivered
\(\frac25\)
of the remaining cookies to a local nursing home.
Next, they gave 3 cookies to some neighborhood kids.
They wrapped up
\(\frac23\)
of the remaining cookies to save for their friends.
After all this, they had 15 cookies left. How many cookies did they bake?
Student Response
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click here to register or sign in
for free access to Extension Student Response.
Activity Synthesis
The purpose of the discussion is to let students voice their reasoning about the direction of the inequality by reasoning about the context. Ask students to share their reasons for choosing the direction of inequality in their solutions. Some students may notice that the algebra in both problems involves multiplying or dividing by a negative number. Honor this observation, but again, the goal is not to turn this observation into a rule for students to memorize and follow. Interpreting the meaning of the solution in the context should remain at the forefront.
As students model real-world situations, questions about the interpretation of the mathematical solution should continue to come up in the conversation. For instance, the amount of the granola bar discount cannot be
$
3.5923, even though this is a solution to the inequality
\(x \geq 3\)
. The value -10 is a solution to Kiran’s inequality, even though he can’t withdraw -10 dollars. Students can argue that negative values for
\(x\)
simply don’t make sense in this context. Some may argue that we should interpret
\(x=\text-10\)
to mean that Kiran deposits
$
10 every month.
Engagement: Develop Effort and Persistence
. Break the class into small discussion groups and then invite a representative from each group to report back to the whole class.
Supports accessibility for: Language; Social-emotional skills; Attention
Representing, Writing, Conversing: MLR8 Discussion Supports.
Use this routine to support whole-class discussion. After a student shares their reasons for the direction of the inequality in their solution, ask students to restate and/or revoice what they heard using mathematical language. Consider providing students time to restate what they hear to a partner, before selecting one or two students to share with the class. Ask the original speaker if their peer was accurately able to restate their thinking. This will help students understand how context determines the direction of inequality.
Design Principle(s): Support sense-making


correct_option_index: 1