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: Explain why addition and subtraction strategies work, using place value and the properties of operations. (Explanations may be supported by drawings or objects.)
problem_activity: Narrative
The purpose of this activity is for students to subtract a one-digit number from a two-digit number. In the previous activity, students shared many ways to subtract including using connecting cubes or base-ten blocks to show decomposing a ten. They build on this understanding as they use base-ten blocks to represent the starting number and subtract an amount that requires them to decompose a ten.
MLR8 Discussion Supports.
Synthesis: Display sentence frames to support students with preparing to explain their thinking in the whole-class discussion. “First, I _____ because . . . .” “I noticed _____ so I . . . .” If necessary, revoice student ideas to demonstrate mathematical language, and invite students to chorally repeat phrases that include relevant vocabulary in context.
Advances: Speaking, Conversing
Representation: Internalize Comprehension.
Synthesis: Invite students to identify which details they think are important to remember. Use the sentence frame: “The next time I subtract, I will know that I need to decompose a ten when . . . .“
Supports accessibility for: Conceptual Processing, Memory
Required Materials
Materials to Gather
Base-ten blocks
Launch
Groups of 2
Give each group access to base-ten blocks.
Activity
“Diego was representing numbers using base-ten blocks. Work with a partner to follow along and see what Diego discovered.”
“Use your blocks first to show what Diego does. Then answer any questions.”
8 minutes: partner work time
Monitor for students who talk about “exchanging” or “trading” a ten for ten ones.
Student Facing
Diego started with 5 tens and 5 ones. Represent Diego’s blocks with the base-ten blocks.
How many does he have?
Diego took away 2 tens.
Draw a representation to show what happened to Diego’s blocks.
Write an equation to show how many Diego has now.
Then, Diego took away 8 ones.
Draw a diagram to show what happened to Diego’s blocks.
Write an equation to show how many Diego has now. Be prepared to explain your reasoning.
Student Response
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Advancing Student Thinking
Some students may get the ones they need, but also keep the ten. Consider asking:
“Why did you add 10 ones to Diego’s blocks?”
“What is the value of the blocks now?”
“When you decompose a tower of ten, what happens to the tower? How could you show this with the base-ten blocks?”
Activity Synthesis
“What did you need to do with the blocks when Diego took away 8 ones?”
Select previously identified students to share.
“What is different about using base-ten blocks compared to the towers of ten?” (With the towers we could break it apart, but with the base-ten blocks we had to give a ten and take out 10 ones.)
“When you subtract by place, sometimes you need to decompose a ten to subtract ones. When we use connecting cubes, we can show those by breaking apart or decomposing a tower of ten.”
“When we use base-ten blocks, we can't break apart the ten into ones, but we can still show decomposing it by replacing 1 ten with 10 ones.”


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