standard_description: Understand that patterns of association can also be seen in bivariate categorical data by displaying frequencies and relative frequencies in a two-way table. Construct and interpret a two-way table summarizing data on two categorical variables collected from the same subjects. Use relative frequencies calculated for rows or columns to describe possible association between the two variables. For example, collect data from students in your class on whether or not they have a curfew on school nights and whether or not they have assigned chores at home. Is there evidence that those who have a curfew also tend to have chores?
problem_activity: Warm-up
The purpose of this warm-up is for students to reason about expressions with negative exponents on a number line. Students explore a common misunderstanding about negative exponents that is helpful to address before scientific notation is used to describe very small numbers.
For students’ reference, consider displaying a number line from a previous lesson that shows powers of 10 on a number line.
Launch
Give students 2 minutes of quiet work time, followed by a whole-class discussion.
Student Facing
Kiran drew this number line.
[IMG]
Andre said, “That doesn’t look right to me.”
Explain why Kiran is correct or explain how he can fix the number line.
Student Response
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Activity Synthesis
The important idea to highlight during the discussion is that the larger the size (or absolute value) of a negative exponent, the closer the value of the expression is to zero. This is because the negative exponent indicates the number of factors that are
\(\frac{1}{10}\)
. For example,
\(10^{\text-5}\)
represents 5 factors that are
\(\frac{1}{10}\)
and
\(10^{\text-6}\)
represents 6 factors that are
\(\frac{1}{10}\)
, so
\(10^{\text-6}\)
is 10 times smaller than
\(10^{\text-5}\)
.
Ask one or more students to explain whether they think the number line is correct and ask for their reasoning. Record and display their reasoning for all to see, preferably on the number line. If possible, show at least two correct ways the number line can be fixed.


aligns: no