standard_description: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
problem_activity: Activity
In this activity students solve a variety of equation types; both in form and number of solutions. After solving the 10 equations, groups sort them into categories of their choosing. The goal of this activity is to encourage students to look at the structure of equations before solving and to build fluency solving complex equations. For example, students who notice that equation D,
\(3 - 4x + 5 = 2(8 - 2x)\)
, has the same number of
\(x\)
s on each side but a different constant know that there are no values of
\(x\)
that make the equation true. Similarly, equation J has the same number of
\(x\)
s on each side and the same constants on each side, meaning that all values of
\(x\)
make the equation true. These up-front observations allow students to avoid spending time working out the steps to re-write the equation into a simpler form where the number of solutions to the equations is easier to see.
Launch
Arrange students in groups of 3. Distribute 10 pre-cut slips from the blackline master to each group. After groups have solved and sorted their equations, consider having groups switch to examine another group’s categories. Leave 3–4 minutes for a whole-class discussion.
Representation: Internalize Comprehension.
Chunk this task into more manageable parts to differentiate the degree of difficulty or complexity by beginning with fewer cards. For example, give students a subset of the cards to start with and introduce the remaining cards once students have completed their initial sort. Some students may benefit from an additional set of cards with more accessible values to start with.
Supports accessibility for: Conceptual processing; Organization
Student Facing
Your teacher will give you some cards.
With your partner, solve each equation.
Then, sort them into categories.
Describe the defining characteristics of those categories and be prepared to share your reasoning with the class.
Student Response
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Activity Synthesis
Select 2–3 groups to share one of their categories’ defining characteristics and which equations they sorted into it. Given the previous activity, the categories “one solution, no solution, all solutions” are likely. Introduce students to the language “infinite number of solutions” if it has not already come up in discussion.
During the discussion, it is likely that students will want to refer to specific parts of an expression. Encourage students to use the words “coefficient” and “variable.” Define the word
constant term
as the term in an expression that doesn't change, or the term that does not have a variable part. For example, in the expression
\(2x-3,\)
the 2 is the coefficient of
\(x\)
, the 3 is a constant, and
\(x\)
is the variable.
Representing, Speaking: MLR8 Discussion Supports.
To support the whole-class discussion, provide the following sentence frames when groups share: “We grouped these equations into the category ____ because_____.” and “Some characteristics of this category are ____.” Invite students to press for details by asking clarifying questions (e.g., “What other features do those equations have in common?” and “Can you explain how to create a different equation that would fall into that category?”). Emphasize language students use to define parts of an expression such as “variable” and “coefficient,” and use this opportunity to define the word “constant term.” This will help students generalize the categories of equations that have one solution, no solution, or “infinitely many solutions.”
Design Principle(s): Support sense-making


aligns: no