few_shots: 
Example 1:
Concept/skill: 
Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.

Problem/activity:
You’re mixing ingredients for cookies. The recipe says to combine 6 tablespoons, or ¾ stick, of butter with 1 cup of sugar. You accidentally mix in a whole stick of butter (8 tablespoons) with the cup of sugar. How can you fix this?


Answer: 
Yes. This problem solves a real-world problem involving mixing ingredients for cookies. A student doing this problem would need to reason about equivalent ratios of butter amounts to sugar amounts.

Example 2:
Concept/skill: 
Apply and extend previous understandings of multiplication and division and of fractions to multiply and divide rational numbers.

Problem/activity:
For each pair of numbers, determine if the values are equivalent. Explain your reasoning for each one.
a.
$$-0.25$$
and
$$\frac{1}{-4}$$
b.
$$-\left ( \frac{1}{4} \right )$$
and
$$\frac{-1}{-4}$$
c.
$$\frac{-1}{4}$$
and
$$-\frac{1}{4}$$


Answer: 
Yes. This problem involves understanding fractions and division to divide rational numbers, such as 1, -4, 4, and -1. This problem also involves an understanding of multiplication: if p and q are integers, then -(p/q) = (-p)/q = p/(-q).

Example 3:
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_000972_pos_0

6

fl_problem_001097_pos_0

7

fl_problem_001392_neg_0

8
standard_description: Find whole-number quotients of whole numbers with up to four-digit dividends and two-digit divisors, using strategies based on place value, the properties of operations, and/or the relationship between multiplication and division. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.
problem_activity: Narrative
The purpose of this activity is for students to consider possible mistakes when multiplying large numbers. Monitor for students who:
revise their answer after examining Kiran’s mistake.
recognize that
\(650 \times 10 = 6,\!500\)
so
\(650 \times 27\)
has to be much greater than 5,850.
can explain why Kiran should be multiplying
\(650 \times 2 \times 10\)
.
recognize that
\(20 \times 50 = 1,\!000\)
so there should be three zeros in the second partial product.
When students determine Kiran's error and make sense of his work, they interpret and critique the work of others (MP3).
MLR1 Stronger and Clearer Each Time.
Synthesis: Before the whole-class discussion, give students time to meet with 2–3 partners to share and get feedback on their response to “what parts of Kiran’s work do you agree and disagree with?” Invite listeners to ask questions, to press for details and to suggest mathematical language. Give students 2–3 minutes to revise their written explanation based on the feedback they receive.
Advances: Writing, Speaking, Listening
Launch
Display or write for all to see.
\(650 \times 27\)
Display each number in a different corner of the room:
14,000
18,000
13,000
19,000
“When I say go, stand in the corner with the number that you think is the most reasonable estimate for
\(650 \times 27\)
. Be prepared to explain your reasoning.”
1 minute: quiet think time
Ask a representative from each corner to explain their reasoning.
“Does anyone want to switch corners?”
Ask a student who switched corners to explain their reasoning.
“Now you are going to find this product and analyze some work.”
Activity
Groups of 2
5–7 minutes: partner work time
Student Facing
Find the value of the product.
[IMG]
Below is Kiran’s work finding the value of the product
\(650 \times 27\)
. Is his answer reasonable? Explain your reasoning.
[IMG]
What parts of the work do you agree with? Be prepared to explain your reasoning.
What parts of the work do you disagree with? Be prepared to explain your reasoning.
Look at your solution to problem 1. Is there anything you want to revise? Be prepared to explain.
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Activity Synthesis
Ask previously identified students to share their thinking.
Display Kiran's work.
“Why doesn’t 5,850 make sense?” (
\(650 \times 10 = 6,\!500 \)
so
\(650 \times 27\)
should be a lot larger than 6,500.)
“What makes sense about Kiran’s work?” (
\(650 \times 2 =1,\!300\)
, but he needs to multiply
\(650\times2\times10\)
.)
Display a student's solution or the image from the student solution.
“How do we know that 17,550 is a reasonable value for the product?” (Because
\(600 \times 30 =18,\!000\)
.)


aligns: no