standard_description: Derive the formula for the sum of a finite geometric series (when the common ratio is not 1), and use the formula to solve problems. For example, calculate mortgage payments.
problem_activity: Activity
The purpose of this activity is for students to think about what they see as “least difficult” and “most difficult” when looking at equations and to practice solving equations. Students also discuss strategies for dealing with “difficult” parts of equations.
Launch
Keep students in the same groups of 2. Give students 3–5 minutes quiet think time to get started and then 5–8 minutes to discuss and work with their partner. Leave ample time for 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 equations:
A.
\(\text{-} \frac56(8+5b)=75+\frac53 b\)
B.
\(\text-\frac12(t+3)-10=\text-6.5\)
C.
\(\frac{10-v}{4}=2(v+17)\)
D.
\(2(4k+3)-13=2(18-k)-13\)
E.
\(\frac{n}{7}-12=5n+5\)
F.
\(3(c-1)+2(3c+1)=\text-(3c+1)\)
G.
\(\frac{4m-3}4=\text{-}\frac{9+4m}8\)
H.
\(p-5(p+4)=p-(8-p)\)
I.
\(2(2q+1.5)=18-q\)
J.
\(2r+49=\text{-}8(\text{-}r-5)\)
Without solving, identify 3 equations that you think would be least difficult to solve and 3 equations you think would be most difficult to solve. Be prepared to explain your reasoning.
Choose 3 equations 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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Student Facing
Are you ready for more?
Mai gave half of her brownies, and then half a brownie more, to Kiran. Then she gave half of what was left, and half a brownie more, to Tyler. That left her with one remaining brownie. How many brownies did she have to start with?
Student Response
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Activity Synthesis
The purpose of this discussion is for students to discuss strategies for solving different types of equations. Some students may have thought that an equation was in the “least difficult” category, while others thought that the same equation was in the “most difficult” category. Remind students that once you feel confident about the strategies for solving an equation, it may move into the “least difficult” category, and recognizing good strategies takes practice and time.
Poll the class for each question as to whether they placed it in the “most difficult” category, “least difficult” category, or if it was somewhere in the middle. Record and display the results of the poll for all to see.
For questions with a split vote, have a group share something that was difficult about it and something that made it seem easy. If there are any questions that everyone thought would be more difficult or everyone thought would be less difficult, ask students why it seemed that way. Ask students, “Were there any equations that were more difficult to solve than you expected? Were there any that were less difficult to solve than you expected?”
Consider asking some of the following questions to further the discussion:
“For equation A, what could we do to eliminate the fraction?” (Multiply each side by the common denominator of 6. Then the terms will all have integer coefficients.)
“Which other equations could we use this strategy for?” (Any equations that had fractions, such as B, C, E, and G.)
“What steps do you need to do to solve equation D? Which other equations are like this one?” (There is a lot of distributing and collecting like terms. F and H also have to distribute several times.)
“What other strategies or steps did you use in solving the equations?”
Representing: MLR3 Clarify, Critique, Correct.
After polling students about the difficulty of each problem, choose the question that was ranked as “most difficult” for students to solve, and display a possible incorrect solution. For example, display
\(2(2q+1.5\)
)
\(=\)
\(4q+1.5\)
, to invite discussion about the distributive property. Invite students to share what makes the question difficult and to name strategies or moves that can be used to solve the equation. Invite students to work with a partner to revise and correct the response. Let them know that they should each be prepared to explain their work. When pairs share their responses with the class, draw students' attention to the language used to describe the steps they took, to clarify their strategies. This will support student understanding of strategies they can use to deal with “difficult” parts of equations.
Design Principle(s): Maximize meta-awareness


aligns: no