Students answer questions about low temperatures recorded in Barrow, Alaska, to understand when to use negative numbers and when to use the absolute values of numbers.Key ConceptsThe absolute value of a number is its distance from 0 on a number line.The absolute value of a number n is written |n| and is read as “the absolute value of n.”A number and the opposite of the number always have the same absolute value. As shown in the diagram, |3| = 3 and |−3| = 3.In general, taking the opposite of n changes the sign of n. For example, the opposite of 3 is –3.In general, taking the absolute value of n gives a number, |n|, that is always positive unless n = 0. For example, |3| = 3 and |−3| = 3.The absolute value of 0 is 0, which is neither positive nor negative: |0| = 0.Goals and Learning ObjectivesUnderstand when to talk about a number as negative and when to talk about the absolute value of a number.Locate the absolute value of a and the absolute value of b on a number line that shows the location of a and b in different places in relation to 0.

Ratios

Type of Unit: Concept

Prior Knowledge

Students should be able to:

Calculate with whole numbers up to 100 using all four operations.
Understand fraction notation and percents and translate among fractions, decimal numbers, and percents.
Interpret and use a number line.
Use tables to solve problems.
Use tape diagrams to solve problems.
Sketch and interpret graphs.
Write and interpret equations.

Lesson Flow

The first part of the unit begins with an exploration activity that focuses on a ratio as a way to compare the amount of egg and the amount of flour in a mixture. The context motivates a specific understanding of the use of, and need for, ratios as a way of making comparisons between quantities. Following this lesson, the usefulness of ratios in comparing quantities is developed in more detail, including a contrast to using subtraction to find differences. Students learn to interpret and express ratios as fractions, as decimal numbers, in a:b form, in words, and as data; they also learn to identify equivalent ratios.

The focus of the middle part of the unit is on the tools used to represent ratio relationships and on simplifying and comparing ratios. Students learn to use tape diagrams first, then double number lines, and finally ratio tables and graphs. As these tools are introduced, students use them in problem-solving contexts to solve ratio problems, including an investigation of glide ratios. Students are asked to make connections and distinctions among these forms of representation throughout these lessons. Students also choose a ratio project in this part of the unit (Lesson 8).

The third and last part of the unit covers understanding percents, including those greater than 100%.

Students have ample opportunities to check, deepen, and apply their understanding of ratios, including percents, with the selection of problems in the Gallery.

Students design and work on their projects in class. They review the project rubric and, as a class, add criteria relevant to their specific projects.Key ConceptsStudents apply their knowledge about ratios to solve a problem. They represent ratios using models such as tables, tape diagrams, double number lines, or graphs.Goals and Learning ObjectivesUse and interpret ratios to solve a problem.Model ratios—including tables, tape diagrams, double number lines, graphs—to represent a problem situation.Articulate strategies, thought processes, and approaches to solving a problem and defend why the solution is reasonable.

This lesson formally introduces and defines a ratio as a way of comparing numbers to one another.Key ConceptsA ratio is defined by the following characteristics:A ratio is a pair of numbers (a:b).Ratios are used to compare two numbers.The value of a ratio a:b is the quotient a ÷ b, or the result of dividing a by b.Other important features of ratios include the following:A ratio does not always tell you the values of quantities being compared.The order of values in a ratio matters.Goals and Learning ObjectivesIntroduce a formal definition of ratio.Use the definition of ratio to solve problems related to comparing quantities.Understand that ratios do not always tell you the values of the quantities being compared.Understand that the order of values in a ratio matters.

Students watch a video in which a double number line is used to solve a problem about getting the right amount of protein mix. Using the double number line is an example of modeling with mathematics, which is Mathematical Practice 4.Key ConceptsA double number line shows corresponding values for two variable quantities with a constant ratio between them. Each pair of tick marks that go together shows a ratio equivalent to all of the other ratios between corresponding tick marks.Goals and Learning ObjectivesWatch an example of students using mathematics to model a relationship between quantities (MP4).Use a double number line to solve a problem.Use a double number line to deepen understanding of equivalence in the context of a relationship between quantities with a constant ratio.SWD: Some students with disabilities will benefit from a preview of the goals in each lesson. Students can highlight the critical features and/or concepts and will help them to pay close attention to salient information.

Students use double number lines to model relationships and to solve ratio problems.Key ConceptsDouble number line diagrams are useful for visualizing ratio relationships between two quantities. They are best used when the quantities have different units. (The unit rate appears paired with 1.) Double number line diagrams help students more easily “see” that there are many equivalent forms of the same ratio.Goals and Learning ObjectivesUnderstand double number line diagrams as a way to visually compare two quantities.Use double number line diagrams to solve ratio problems.

Students are asked to fix a botched mixture that does not follow a given recipe. To fix the mixture, students must find a ratio of eggs to flour that is equivalent to 2:3, but without explicit instruction on the concept of equivalent ratios.Key ConceptsStudents are invited to investigate the underlying idea of equivalent ratios by “correcting” the ratio between two ingredients in a botched mixture that does not follow a given recipe.Goals and Learning ObjectivesExplore a problem based on a recipe with two ingredients.Share approaches, clarify reasoning, and develop clear explanations of how to know a mixture has the right balance of ingredients.

Students work with a set of cards showing different ways of expressing ratios, including both part-part statements and part-whole statements. They group the cards that show the same ratio of boys to girls, but without the explicit use of the term equivalent.Key ConceptsRatios can be represented in a:b form, as fractions, as decimals, as factors, and in words; they can be expressed in part-part statements or in part-whole statements.Goals and Learning ObjectivesGroup cards showing ratios that are equivalent but expressed in different forms.

Students work with a set of cards showing different ways of expressing ratios numerically. They group the cards showing equivalent ratios and then order the groups from least to greatest value.Key ConceptsIt can be hard to compare the values of ratios represented in different forms (e.g., a:b, decimal, fraction, a to b). Simplifying ratios makes it easier to compare and order their values.Goals and Learning ObjectivesIdentify ratios that are equivalent but expressed differently.Simplify ratios in order to group and order cards efficiently and successfully.

Students use informal methods of their own choosing to find percents of randomly generated monetary values.Key ConceptsMany approaches work for solving percent problems. This lesson focuses on experimenting with a range of approaches and understanding why and how multiple approaches yield correct results.Goals and Learning ObjectivesFind a percent of a given quantity.Find a quantity given a part and the percent that part is of the whole.Use percents in money calculations.

Gallery OverviewAllow students who have a clear understanding of the content thus far in the unit to work on Gallery problems of their choosing. You can then use this time to provide additional help to students who need review of the unit's concepts or to assist students who may have fallen behind on work.Gallery DescriptionsWork on Your ProjectStudents will work on their project with their group and evaluate their progress using the rubric.Equivalent RatiosSometimes ratios that are equivalent don’t look equivalent at first. Students will use their ratio detective skills to identify equivalent ratios, and then they will choose a model to represent a set of equivalent ratios.Three FarmersTough times on the farm mean three farmers are sharing a seed purchase. Students will make sure each farmer gets the right amount of seed.The DanceEveryone is excited about the upcoming school dance, and two students discuss the ratio of boys to girls. Students will evaluate their statements and decide if their statements are true.The Adults at SchoolWho are the adults who work at school? Students will represent and investigate ratios of teachers to non-teaching staff, including adults at their own school.Sports ReportersReporters are sometimes wrong. Students will check the math in two reports about soccer matches at Estadio Azteca in Mexico City.Screen ChallengeThe aspect ratio of movie screens and TV screens has a direct impact on viewers’ experience. Students will explore aspect ratios in this activity.Election ResultsOops! A newspaper made an error in a report about the local election results. Students will find and fix the error.Birthday at the MoviesMia’s family is treating her whole class to a movie for her birthday! Students will calculate how much the tickets will cost.Dinner ReservationsIt’s graduation night! Students will calculate how many tables a restaurant needs for a party of 26 people.Birth MonthsStudents will investigate the percent of students in a class who have birthdays in each month.

This lesson introduces the concept of a glide ratio and encourages students to use appropriate tools strategically (Mathematical Practice 5). Students use tape diagrams, double number lines, ratio tables, graphs, and equations to represent glide ratios.Key ConceptsA glide ratio for an object or an organism in flight is the ratio of forward distance to vertical distance (in the absence of power and wind). For a given object or organism that glides, this ratio has a constant value and is treated as a feature of the object or organism.Goals and Learning ObjectivesUnderstand the concept of a glide ratio.Make connections within and between different ways of representing ratios.

Student groups continue to make their presentations, provide feedback for other students’ presentations, and get evaluated on their listening skills.Key ConceptsIn this culminating event, students continue presenting their project plan and solution to the class. The presentation allows students to explain their problem-solving plan, to communicate their reasoning, and to construct a viable argument about a mathematical problem. Students also listen to other project presentations and provide feedback to the presenters. Listeners have the opportunity to critique the mathematical reasoning of others.Goals and Learning ObjectivesPresent project to the class.Give feedback on other project presentations.Exhibit good listening skills.Reflect on the problem-solving process.

Students interpret multiple categories of data about a hypothetical village population that represents the global population. They determine whether percent statements about the data are true or false.Key ConceptsData presented in multiple formats can be investigated using percent statements that facilitate comparisons between different parts of a whole. In using percents to interpret data, it is essential to be clear about what the part is and what the whole is. The whole in this lesson is a representative sample of the global population, which is used as a model for investigating variation across the population.Goals and Learning ObjectivesInterpret data presented in different formats in terms of percents.Identify percent statements as true or false, if possible, and explain the decision.Modify false percents statements to make them true.

Students use percents greater than 100% to solve problems about rainfall, revenue, snowfall, and school attendance.Key ConceptsPercents greater than 100% are useful in making comparisons between the values of a single quantity at two points in time. When a later value is more than 100% of an earlier value, it means the quantity has increased over time. This percent comparison can be used to find unknown values, whether the earlier or later value is unknown.Goals and Learning ObjectivesUnderstand the meaning of a percent greater than 100% in real-world situations.Use percents greater than 100% to interpret situations and solve problems.

Students focus on interpreting, creating, and using ratio tables to solve problems. They also relate ratio tables to graphs as two ways of representing a relationship between quantities.Key ConceptsRatio tables and graphs are two ways of representing relationships between variable quantities. The values shown in a ratio table give possible pairs of values for the quantities represented and define ordered pairs of coordinates of points on the graph representing the relationship. The additive and multiplicative structure of each representation can be connected, as shown: Goals and Learning ObjectivesComplete ratio tables.Use ratio tables to compare ratios and solve problems.Plot values from a ratio table on a graph.Understand the connection between the structure of ratio tables and graphs.

Student groups make their presentations, provide feedback for other students’ presentations, and get evaluated on their listening skills.Key ConceptsIn this culminating event, students must present their project plan and solution to the class. The presentation allows students to explain their problem-solving plan, to communicate their reasoning, and to construct a viable argument about a mathematical problem. Students also listen to other project presentations and provide feedback to the presenters. Listeners have the opportunity to critique the mathematical reasoning of others.Goals and Learning ObjectivesPresent project to the class.Give feedback on other project presentations.Exhibit good listening skills.

Students choose a project idea and a partner or group. They write a proposal for the project.Key ConceptsProjects engage students in the applications of mathematics. It is important for students to apply mathematical ways of thinking to solve rich problems. Students are more motivated to understand mathematical concepts if they are engaged in solving a problem of their own choosing. In this lesson, students are challenged to identify an interesting mathematical problem and to choose a partner or a group to work with collaboratively in order to solve that problem. Students gain valuable skills in problem solving, reasoning, and communicating mathematical ideas with others.Goals and Learning ObjectivesIdentify a project ideaIdentify a partner or group to work with collaboratively on a math project

Students begin the lesson with a critique of their own work on the Self Check using questions and comments from you to reflect on their work. They then critique three examples of student work on the task, each with its own tools for modeling the given relationship between quantities. Finally, they apply what they learned to a closely related problem.Key ConceptsStudents reflect on their work and connect different ways of representing ratio relationships: tape diagrams, double number lines, and ratio tables.Goals and Learning ObjectivesUse teacher comments to refine solution strategies for ratio problems.Deepen understanding of ratio relationships.Synthesize and connect strategies for representing and investigating ratio relationships.Critique given student models created to solve ratio problems.Apply deepened understanding of ratio relationships to a new ratio problem.

Students use tape diagrams to model relationships and solve problems about types of DVDs.Key ConceptsTape diagrams are useful for visualizing ratio relationships between two (or more) quantities that have the same units. They can be used to highlight the multiplicative relationship between the quantities.Goals and Learning ObjectivesUnderstand tape diagrams as a way to visually compare two or more quantities.Use tape diagrams to solve ratio problems.