options: Apply and extend previous understandings of arithmetic to algebraic expressions.

Write and interpret numerical expressions.

Interpret the structure of expressions.

Represent and solve equations and inequalities graphically.

Reason about and solve one-variable equations and inequalities.

Add and subtract within 20.

Understand the connections between proportional relationships, lines, and linear equations.

Represent and solve problems involving addition and subtraction.

Solve real-life and mathematical problems using numerical and algebraic expressions and equations.

Gain familiarity with factors and multiples.

Represent and analyze quantitative relationships between dependent and independent variables.

Analyze and solve linear equations and pairs of simultaneous linear equations.

Rewrite rational expressions.

Work with addition and subtraction equations.

Create equations that describe numbers or relationships

Solve systems of equations.

Use the four operations with whole numbers to solve problems.

Work with radicals and integer exponents.

Understand solving equations as a process of reasoning and explain the reasoning.

Analyze patterns and relationships.

Understand properties of multiplication and the relationship between multiplication and division.

Generate and analyze patterns.

Perform arithmetic operations on polynomials.

Work with equal groups of objects to gain foundations for multiplication.

Use properties of operations to generate equivalent expressions.

Represent and solve problems involving multiplication and division.

Understand the relationship between zeros and factors of polynomials.

Solve equations and inequalities in one variable.

Understand addition as putting together and adding to, and understand subtraction as taking apart and taking from.

Write expressions in equivalent forms to solve problems.

Solve problems involving the four operations, and identify and explain patterns in arithmetic.

Use polynomial identities to solve problems.

Multiply and divide within 100.

Understand and apply properties of operations and the relationship between addition and subtraction.
problem_activity: Optional activity
In this activity, students solve a variety of systems of equations, some involving fractions, some involving substitution, and some involving inspection. This gives students a chance to practice using the methods they have learned in this section for solving systems of equations to solidify that learning. Some of the systems listed are ones students could have used in an earlier activity in this lesson, to describe the situations there. In the discussion, students compare the systems here to the ones they wrote in that activity and interpret the answer in that context.
Launch
Keep students in groups of 2. Allow students 5–7 minutes of partner work time followed by a whole-class discussion.
Representation: Internalize Comprehension
. Activate or supply background knowledge. Allow students to use calculators to ensure inclusive participation in the activity.
Supports accessibility for: Memory; Conceptual processing
Student Facing
Here are a lot of systems of equations:
\(\begin{cases} y=\text-2x+6 \\ y=x-3 \end{cases}\)
\(\begin{cases} y=5x-4 \\ y=4x+12 \end{cases}\)
\(\begin{cases} y=\frac23x-4 \\ y=\text-\frac43x+9 \end{cases}\)
\(\begin{cases} 4y + 7x = 6 \\ 4y+7x = \text-5 \end{cases}\)
\(\begin{cases} y=x - 6\\ x=6 + y \end{cases}\)
\(\begin{cases} y=0.24x\\ y=0.18x+0.9 \end{cases}\)
\(\begin{cases} y=4.5x+15 \\ y=5x+12.5 \end{cases}\)
\(\begin{cases} y=3x \\ x+y=52 \end{cases}\)
Without solving, identify 3 systems that you think would be the least difficult for you to solve and 3 systems you think would be the most difficult. Be prepared to explain your reasoning.
Choose 4 systems to solve. At least one should be from your "least difficult" list and one should be from your "most difficult" list.
Student Response
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Activity Synthesis
There are two key takeaways from this discussion. The first is to reinforce that some systems can be solved by reasoning whether its possible for a solution to one equation to also be a solution to another. The second takeaway is that there are some systems that students will only be able to solve after learning techniques in future grades.
For each problem, ask students to indicate if they identified the system as least or most difficult. Record the responses for all to see.
Bring students' attention to this system:
\(\begin{cases} 4y + 7x = 6 \\ 4y+7x = \text-5 \end{cases}\)
Ask students what the two equations in the system have in common to each other and to think about whether a solution to the first equation could also be a solution to the second. One can reason there is no solution because
\(4y+7x\)
cannot be equal to both 6 and -5.
Ask students to return to the earlier activity and see if they can find any of those systems in these problems. (Lin's family ride is the sixth system. Noah's kayaking trip is the seventh system. Diego's baking is the eighth system.) After students notice the connection, invite students who chose those systems to solve to interpret the numerical solutions in the contexts from the earlier activity.
Students may be tempted to develop the false impression that all systems where both equations are given as linear combinations can be solved by inspection. Conclude the discussion by displaying this system that students defined in the last activity about sugar and flour:
\(\begin{cases} 0.8x+0.5y = 9 \\ x+y = 15 \end{cases}\)
Tell students that this system has one solution and they will learn more sophisticated techniques for solving systems of equations like this in future grades.
Speaking, Listening, Conversing: MLR8 Discussion Supports.
Before the whole-class discussion, use this routine to give students an opportunity to discuss their reasons for labeling systems of equations as “least difficult” or “most difficult.” Provide the following sentence frame: “_____ is the least/most difficult to solve because _____.” Encourage listeners to press for detail by asking questions such as “What would make that problem easier to solve?”; “What do your least/most difficult problems have in common?” This will help students make connections between the structures of given systems of equations, and possible strategies they can use to solve them.
Design Principle(s): Cultivate conversation; Maximize meta-awareness


correct_option_index: 11