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 to multiply a fraction or whole number by a fraction.

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: 
No. The expressions shown in this problem do not involve multiplying fractions with other fractions, nor whole numbers with fractions.

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_neg_0

7

fl_problem_001392_neg_0

8
standard_description: Construct a function to model a linear relationship between two quantities. Determine the rate of change and initial value of the function from a description of a relationship or from two (x, y) values, including reading these from a table or from a graph. Interpret the rate of change and initial value of a linear function in terms of the situation it models, and in terms of its graph or a table of values.
problem_activity: Activity
If students also use technology to create the tables, they are using appropriate tools strategically (MP5).
Launch
Provide access to graphing technology. Students may need some assistance adjusting their graphing window to see the relevant features of each graph. Either help them set the window before they start to a domain of
\(\text-2 \le x \le 8\)
and range of
\(\text-60 \le y \le 600\)
, or wait until they have attempted to graph at least one function and remind them of what they have learned about changing the graphing window.
Student Facing
Each function represents the amount in a bank account after
\(t\)
weeks.
\(A(t) = 500\)
\(B(t) = 500 + 40t\)
\(C(t) = 500 - 40t\)
\(D(t) = 500 \boldcdot (1.5)^t\)
\(E(t) = 500 \boldcdot (0.75)^t\)
Make a table for each bank account showing the money in the account at 0, 1, 2, and 3 weeks.
Describe in words how the money in the account is changing week by week.
Use technology to create a graph of each function. How can you see your description in each graph?
Student Response
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Activity Synthesis
Focus the discussion on the connection between the equations, descriptions and graphs. Discuss questions such as:
“What do all functions have in common?” (The vertical intercept is 500, each bank account starts with $500)
“How does the money change each week? How do we see this change in the graph?"
“How are
\(B\)
and
\(C\)
the same and different?” (They are the same because they are each linear, and each start with
$
500 and change by
$
40 per week. They are different because B increases and C decreases (or the rate of change is positive versus negative.)
“How are
\(D\)
and
\(E\)
the same and different?” (They are the same because they are each exponential, and each start with
$
500. They are different because
\(D\)
increases and
\(E\)
decreases (or the growth factor is greater than 1 versus less than 1.))


aligns: no