few_shots: 
Example:
Concept/skill: 
Prove that, given a system of two equations in two variables, replacing one equation by the sum of that equation and a multiple of the other produces a system with the same solutions.

Problem/activity:
Problem 1
The table below contains single equations in a single variable, single equations in two variables, and pairs of simultaneous equations in two variables. Check the appropriate box to show whether there is no solution, exactly 1 solution, or if there is an infinite number of solutions.
|                                                          | **           No solution          ** | **           Exactly 1 solution          ** | **           Infinite number of solutions          ** |
|----------------------------------------------------------|--------------------------------------|---------------------------------------------|-------------------------------------------------------|
|                       $${9=4x+7}$$                       |                                      |                                             |                                                       |
|                       $${y=3y+5}$$                       |                                      |                                             |                                                       |
|                    $${y={x\over2}}$$                     |                                      |                                             |                                                       |
|                     $${3x+6y-9=0}$$                      |                                      |                                             |                                                       |
|    $${x=y}$$                        $${1.25x=1.25y}$$    |                                      |                                             |                                                       |
| $${9.9=6x+8y}$$                        $${9x=2.5y-8.8}$$ |                                      |                                             |                                                       |
| $${11x-2y=1.5}$$                        $${11x-2y=2.5}$$ |                                      |                                             |                                                       |
Problem 2
Kim has a small container and a large container as shown.
[IMG]
It takes 16 of the small containers to fill the large container. Three small containers leave 1.95 gallons of space in the big container.
What is the size of each of the two containers?


Answer: 
No. Completing neither of these problems requires replacing one equation by the sum of that equation and a multiple of the other equation.

Now, determine whether the following problem or activity can enable students to understand the concepts or skills in the provided description.

shot_info: fl_problem_001392_neg_0

8
standard_description: Prove the addition and subtraction formulas for sine, cosine, and tangent and use them to solve problems.
problem_activity: Narrative
The purpose of this activity is for students to solve two-step problems without the scaffold of having the first step explicitly stated. Students solve in a way that makes sense to them and might use diagrams to help them make sense of the story. In the synthesis, the tape diagram is highlighted.
MLR7 Compare and Connect.
Synthesis: Invite group to prepare a visual display that shows the strategy they used to solve the story problems. Encourage students to include details that will help others interpret their thinking. For example, using labels, notes, diagrams, or drawings. Give students time to investigate each other’s work. During the whole-class discussion, ask students, “What did the representations have in common?”, “How were they different?” and “Did anyone solve the problem the same way, but would explain it differently?”
Advances: Representing, Conversing
Launch
Groups of 2
“With a partner, choose a problem from the first activity to solve. Discuss how the diagram can help you think about the problem.”
4 minutes: partner work time
Activity
“Now you will be solving a few money problems on your own.”
“Use a diagram if it helps you make sense of the story.”
10 minutes: independent work time
Monitor for students who use a diagram to represent and solve the problem about Tyler, Andre, and Noah.
Student Facing
For each problem, show your thinking. Write your final answer using the \$. Use a diagram if it helps.
Mai has \$27, Elena has \$48, and Jada has \$16. How much money do they have altogether?
Tyler has \$45, Andre has \$36, and Noah has \$28. How much less money does Tyler have than Andre and Noah combined?
Lin has \$19. Together, Lin and Han have \$45. Then Han gets \$17 more. How much money does Han have now?
Student Response
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Advancing Student Thinking
If students want to represent the story with a diagram or equation but need support to start, consider asking:
“What is the story about? How could you break the problem into smaller parts?”
“How could you use a diagram or equation to represent the smaller parts?”
Activity Synthesis
Invite previously identified students to share the diagram for comparing Tyler's money to Andre's and Noah's money.
“How does this diagram represent the story?” (It shows Tyler's amount and then the combined amount of Andre and Noah. I can see that Tyler has less than Andre and Noah and that I need to add Andre's amount and Noah's amount and then subtract Tyler's amount from that.)


aligns: no