standard_description: Write, read, and evaluate expressions in which letters stand for numbers.
problem_activity: Activity
The goal of this activity is to help students flexibly transition between different notations for powers of 10 and introduce the property of multiplication of values with the same base. Students observe that
\(10^n \boldcdot 10^m = 10^{n+m}\)
for values of
\(n\)
and
\(m\)
that are positive integers. The second question hints at the reasoning that will extend exponent rules to include zero exponents, but students will investigate that more deeply in a later lesson.
Notice students who need help writing the general rule in in terms of
\(n\)
and
\(m\)
. You might ask, “What patterns did you notice with the exponents in the table? So if the exponents are
\(n\)
and
\(m\)
, how do you write what you did with the exponents?”
Launch
Give students 1 minute of quiet think time to complete the first unfinished row in the table before asking 1–2 students to share and explain their answers. When it is clear that students know how to complete the table, explain to them that they can skip one entry in the table, but they have to be able to explain why they skipped it. Give students 7–8 minutes to work before a brief whole-class discussion.
Student Facing
Complete the table to explore patterns in the exponents when multiplying powers of 10. You may skip a single box in the table, but if you do, be prepared to explain why you skipped it.
|          expression           |                                          expanded                                          | single power of 10 |
|-------------------------------|--------------------------------------------------------------------------------------------|--------------------|
|    \(10^2 \boldcdot 10^3\)    |                     \((10 \boldcdot 10)(10\boldcdot 10 \boldcdot 10)\)                     |      \(10^5\)      |
|    \(10^4 \boldcdot 10^3\)    |                                                                                            |                    |
|    \(10^4 \boldcdot 10^4\)    |                                                                                            |                    |
|                               | \((10 \boldcdot 10 \boldcdot 10)(10 \boldcdot 10 \boldcdot 10 \boldcdot 10 \boldcdot 10)\) |                    |
| \(10^{18} \boldcdot 10^{23}\) |                                                                                            |                    |
If you chose to skip one entry in the table, which entry did you skip? Why?
Use the patterns you found in the table to rewrite
\(10^n \boldcdot 10^m\)
as an equivalent expression with a single exponent, like
\(10^{\boxed{\phantom{3}}}\)
.
Use your rule to write
\(10^4 \boldcdot 10^0\)
with a single exponent.  What does this tell you about the value of
\(10^0\)
?
The state of Georgia has roughly
\(10^7\)
human residents. Each human has roughly
\(10^{13}\)
bacteria cells in his or her digestive tract. How many bacteria cells are there in the digestive tracts of all the humans in Georgia?
Student Response
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Student Facing
Are you ready for more?
There are four ways to make
\(10^4\)
by multiplying powers of 10 with smaller, positive exponents.
\(\displaystyle 10^1 \boldcdot 10^1 \boldcdot 10^1 \boldcdot 10^1\)
\(\displaystyle 10^1 \boldcdot 10^1 \boldcdot 10^2\)
\(\displaystyle 10^1 \boldcdot 10^3\)
\(\displaystyle 10^2 \boldcdot 10^2\)
(This list is complete if you don't pay attention to the order you write them in. For example, we are only counting
\(10^1 \boldcdot 10^3\)
and
\(10^3 \boldcdot 10^1\)
once.)
How many ways are there to make
\(10^6\)
by multiplying smaller powers of 10 together?
How about
\(10^7\)
?
\(10^8\)
?
Student Response
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for free access to Extension Student Response.
Activity Synthesis
Create and post visual displays showing the exponent rules for reference throughout the unit, with one visual display for each rule. The visual display could include an example to illustrate how the rule works, along with visual aids and use of color. Here is a sample visual display:
[IMG]
Explain the visual display to students and display it for all to see throughout the unit.
Writing: MLR3 Clarify, Critique, Correct.
Present a hypothetical student statement that represents a misunderstanding of the exponent rule, such as “
\(10^2 ⋅ 10^3 = 10^6 \)
because
\(2⋅3 = 6\)
.” Prompt discussion by asking, “Do you agree with the statement? Why or why not?” Then, ask students to individually write an improved statement. Improved responses should include connections between the representations of a single expression, expanded form, and the single power of 10. This will help students evaluate, and improve on, the written mathematical arguments of others and highlight why
\(10^n\boldsymbol\cdot 10^m=10^{n+m}\)
.
Design Principle(s): Maximize meta-awareness.


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