few_shots: 
Example 1:
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?


Concept/skill: 
Recognize and represent proportional relationships between quantities.

Answer: 
No. Usually problems that teach recognizing and representing proportional relationships between quantities involve deciding whether two quantities are in a proportional relationship or identifying the constant of proportionality, and then representing proportional relationships by equations or explaining proportional relationship using coordinate graphs.

Example 2:
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
$$-\frac{1}{4}$$


Concept/skill: 
Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.

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

Example 3:
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?


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.

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, does the problem or activity shown below enable students to learn the full intent of the following concept or skill?

shot_info: fl_problem_000972_neg_0

6

fl_problem_001097_neg_0

7

fl_problem_001392_neg_0

8
standard_description: Perform operations with numbers expressed in scientific notation, including problems where both decimal and scientific notation are used. Use scientific notation and choose units of appropriate size for measurements of very large or very small quantities (e.g., use millimeters per year for seafloor spreading). Interpret scientific notation that has been generated by technology.
problem_activity: Activity
Students learn the definition of scientific notation and practice using it. Students attend to precision when determining whether or not a number is in scientific notation and converting numbers into scientific notation (MP6).
Throughout the activity, students use the usual
\(\boldcdot \)
symbol to indicate multiplication, but the discussion establishes the standard way to show multiplication in scientific notation with the
\(\times\)
symbol. Although these materials tend to avoid the
\(\times\)
symbol because it is easy to confuse with
\(x\)
, the ubiquitous use of
\(\times\)
for scientific notation outside of these materials necessitates its use here.
Launch
Tell students, “Earlier, we examined the speed of light through different materials. We zoomed into the number line to focus on the interval between
\(2.0 \times 10^8\)
meters per second and
\(3.0 \times 10^8\)
meters per second as shown in the figure.” Display the following image notation for all to see.
[IMG]
Tell students, “We saw that the speed of light through ice was
\(2.3 \times 10^8\)
meters per second. This way of writing the number is called
scientific notation
. Scientific notation is useful for understanding very large and very small numbers.”
Display and explain the following definition of scientific notation for all to see.
A number is said to be in scientific notation when it is written as a product of two factors:
The first factor is a number greater than or equal to 1, but less than 10, for example 1.2, 8, 6.35, or 2.008.
The second factor is an integer power of 10, for example
\(10^8\)
,
\(10^\text{-4}\)
, or
\(10^{22}\)
.
Carefully consider the first question and go through the list of numbers as a class, frequently referring to the definition to decide whether the number is written in scientific notation. When all numbers written in scientific notation have been circled, consider demonstrating or discussing how a number that was not circled could be written in scientific notation. Then, ask students to complete the second question (representing the other numbers in scientific notation). Leave 3–4 minutes for a whole-class discussion.
Student Facing
The table shows the speed of light or electricity through different materials.
|       material       | speed (meters per second) |
|----------------------|---------------------------|
|        space         |        300,000,000        |
|        water         |   \(2.25 \times 10^8\)    |
| copper (electricity) |        280,000,000        |
|       diamond        |    \(124 \times 10^6\)    |
|         ice          |    \(2.3 \times 10^8\)    |
|      olive oil       |    \(0.2 \times 10^9\)    |
Circle the speeds that are written in scientific notation. Write the others using scientific notation.
[IMG]
Student Response
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Activity Synthesis
Tell students that almost all books and information about scientific notation use the
\(\times\)
symbol to indicate multiplication between the two factors, so from now on, these materials will use the
\(\times\)
symbol in this same way. Display
\((2.8) \boldcdot 10^8\)
for all to see, and then rewrite it as
\(2.8 \times 10^8\)
. Emphasize that using
\(\boldcdot \)
is not incorrect, but that
\(\times\)
is the most common usage.
Ask students to come up with at least two examples of numbers that are
not
in scientific notation. Select responses that highlight the fact that the first factor must be between 1 and 10 and other responses that highlight that one of the factors must be an integer power of 10. Make sure students recognize what does and does not count as scientific notation.
Also make sure students understand how to write an expression that may use a power of 10 but is not in scientific notation as one that is in scientific notation. Consider using the speed of light through diamond as an example. Ask a series of questions such as:
“In
\(124 \times 10^6\)
, how must we write the first factor for the expression to be in scientific notation?” (A number between 1 and 10, so 1.24 in this case)
“How can we rewrite 124 as an expression that has 1.24?” (Write it as
\(1.24 \times 100\)
or
\(1.24 \times 10^2\)
)
“What is the equivalent expression in scientific notation?” (
\(1.24 \times 10^2) \times 10^6\)
, which is
\(1.24 \times 10^8\)
)
Representation: Develop Language and Symbols.
Create a display of important terms and vocabulary.  Include the following term and maintain the display for reference throughout the unit: scientific notation. Invite students to suggest language or diagrams to include on the display that will support their understanding of this term.
Supports accessibility for: Memory; Language
Writing: MLR3 Clarify, Critique, Correct.
Display a hypothetical student statement that represents a misunderstanding about how to write values in scientific notation, such as: “To write the speed of light through a diamond is
\(12.4 \times 10^7\)
.” Ask pairs of students to critique the response by asking, “Do you agree with the author? Why or why not?”Invite students to write feedback to the author that identifies the reasoning error and how to improve the statement. Listen for students who include in their feedback a need for the first factor to be between 1 and 10. This helps students evaluate, and improve on, the written mathematical arguments of others.
Design Principle(s): Maximize meta-awareness; Support sense-making


aligns: yes