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

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.

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

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

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

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

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.

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.

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.

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.

Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.
problem_activity: Activity
This activity is intended to build confidence and facility in writing an equation for a proportional relationship. Students build on their understanding that measurement conversions can be represented by proportional relationships, which they studied in an earlier lesson and will revisit in future lessons. Students are expected to use methods developed earlier: organize data in a table, write and solve an equation to determine the constant of proportionality, and use repeated reasoning (MP8) to arrive at an equation. In addition, they are expected to identify the relationship between the constant of proportionality when going from centimeters to meters and vice versa (reciprocals). Since students have already explored a similar relationship (centimeters and millimeters) in a previous lesson, this activity may go very quickly.
As students work, look for students writing an equation like
\(100k = 1\)
(for table 2) as a step to finding the constant of proportionality. Encourage them to say how they would solve the equation. Ask students to say why using this equation makes sense in the scenario.
Launch
Introduce the task: “In a previous lesson, you examined the relationship between millimeters and centimeters. Today we will examine the relationship between centimeters and meters.”
Student Facing
There are 100 centimeters (cm) in every meter (m).
{"table": [{"_attributes": {"border": "1"}, "thead": [{"tr": [{"th": [{"_attributes": {"scope": "col"}, "_value": "length (m)"}, {"_attributes": {"scope": "col"}, "_value": "length (cm)"}]}]}], "tbody": [{"tr": [{"td": [{"_value": "1"}, {"_value": "100"}]}, {"td": [{"_value": "0.94"}, {}]}, {"td": [{"_value": "1.67"}, {}]}, {"td": [{"_value": "57.24"}, {}]}, {"td": [{"span": [{"_attributes": {"class": ["math", "math-repaired"], "data-png-file-id": "50"}, "_value": "\\(x\\)"}]}, {}]}]}]}]}
{"table": [{"_attributes": {"border": "1"}, "thead": [{"tr": [{"th": [{"_attributes": {"scope": "col"}, "_value": "length (cm)"}, {"_attributes": {"scope": "col"}, "_value": "length (m)"}]}]}], "tbody": [{"tr": [{"td": [{"_value": "100"}, {"_value": "1"}]}, {"td": [{"_value": "250"}, {}]}, {"td": [{"_value": "78.2"}, {}]}, {"td": [{"_value": "123.9"}, {}]}, {"td": [{"span": [{"_attributes": {"class": ["math", "math-repaired"], "data-png-file-id": "29"}, "_value": "\\(y\\)"}]}, {}]}]}]}]}
Complete each of the tables.
For each table, find the constant of proportionality.
What is the relationship between these constants of proportionality?
For each table, write an equation for the proportional relationship. Let
\(x\)
represent a length measured in meters and
\(y\)
represent the same length measured in centimeters.
Student Response
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Student Facing
Are you ready for more?
How many cubic centimeters are there in a cubic meter?
How do you convert cubic centimeters to cubic meters?
How do you convert the other way?
Student Response
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Activity Synthesis
Invite students to share their answers. These questions can guide the discussion:
"How can we find an equation for each table?"
"Where does the constant of proportionality occur in the table and equation?"
"What is the relationship between the two constants of proportionality? How can you use the equations to see why this should be true?"
The equations can help students see why the constants of proportionality are reciprocals:
\(\displaystyle y = 100x\)
\(\displaystyle \left(\frac{1}{100}\right)y = \frac{1}{100} \boldcdot (100x)\)
\(\displaystyle \left(\frac{1}{100}\right)y = x\)
\(\displaystyle x = \left(\frac{1}{100}\right)y\)
This line of reasoning illustrated above should be accessible to students, because it builds on grade 6 work with expressions and equations.
Ask students to interpret the meaning of the equations in the context: "What do the equations tell us about the conversion from meters to centimeters and back?"
Given the length in meters, to find the length in centimeters, multiply the number of centimeters by 100.
Given the length in centimeters, to find the the length in meters, multiply the number of meters by
\(\frac{1}{100}\)
.
Engagement: Develop Effort and Persistence.
Encourage and support opportunities for peer interactions. Prior to the whole-class discussion, invite students to share their work with a partner. Display sentence frames to support student conversation such as: “First, I _____ because….,” “I noticed _____ so I….,” “Why did you . . .?,” and “I agree/disagree because….”
Supports accessibility for: Language; Social-emotional skills
Speaking: MLR8 Discussion supports.
Provide students with sentence frames such as “I found the constant of proportionality by _____” to help explain their reasoning. Revoice student ideas to model mathematical language use by restating a response as a question in order to clarify, and apply appropriate language.
Design Principle(s): Maximize linguistic and cognitive awareness


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