options: Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.

Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.
problem_activity: Activity
Students have just learned the meaning of the
\(y\)
-intercept for a line and have been interpreting slope in context. In this activity, they investigate the
\(y\)
-intercept and slope together and investigate what happens when their values are switched.
In contexts like this one, the
\(y\)
-intercept and the slope come with natural units and understanding this can help graph accurately. Specifically, the
\(y\)
-intercept is the number of pages Lin read before she starts gathering data for the graph. The slope, on the other hand, is a rate: it’s the number of pages Lin reads
per day
.
Watch for students who understand the source of Lin’s error (confusing the
\(y\)
-intercept with the slope) and invite them to share this observation during the discussion.
Launch
Work time followed by whole-class discussion.
Representation: Internalize Comprehension.
Use MLR6 Three Reads to supporting reading comprehension of the word problem. Use the first read to orient students to the situation. Ask students to describe what the situation is about without using numbers (Lin’s reading assignment). Use the second read to identify quantities and relationships. Ask students what can be counted or measured without focusing on the values. Listen for and amplify the important quantities that vary in relation to each other in this situation: first 30 pages and 40 pages each day. After the third read, ask students to brainstorm possible strategies to answer the question, “What does the vertical intercept mean in this situation?”
Supports accessibility for: Language; Conceptual processing
Speaking: MLR8 Discussion Supports.
Use this to amplify mathematical uses of language to communicate about vertical intercepts, slope, and constant rate. Invite students to use these words when describing their ideas. Ask students to chorally repeat phrases that include these words in context.
Design Principle(s): Support sense-making, Optimize output (for explanation)
Student Facing
Lin has a summer reading assignment. After reading the first 30 pages of the book, she plans to read 40 pages each day until she finishes. Lin makes the graph shown here to track how many total pages she'll read over the next few days.
After day 1, Lin reaches page 70, which matches the point
\((1,70)\)
she made on her graph. After day 4, Lin reaches page 190, which does not match the point
\((4,160)\)
she made on her graph. Lin is not sure what went wrong since she knows she followed her reading plan.
[IMG]
Sketch a line showing Lin's original plan on the axes.
What does the
vertical intercept
mean in this situation? How do the vertical intercepts of the two lines compare?
What does the slope mean in this situation? How do the slopes of the two lines compare?
Student Response
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Student Facing
Are you ready for more?
Jada's grandparents started a savings account for her in 2010. The table shows the amount in the account each year.
If this relationship is graphed with the year on the horizontal axis and the amount in dollars on the vertical axis, what is the vertical intercept? What does it mean in this context?
| year | amount in dollars |
|------|-------------------|
| 2010 |        600        |
| 2012 |        750        |
| 2014 |        900        |
| 2016 |       1050        |
Student Response
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click here to register or sign in
for free access to Extension Student Response.
Activity Synthesis
Ask students:
“How did your graph compare to Lin’s?” (It is steeper but starts off at 30 instead of 40 pages.)
“Which point does your graph have in common with Lin’s?” (The point
\((1,70)\)
, 70 pages read after one day.)
Invite selected students to share what’s the likely source of Lin’s error (confusing the
\(y\)
-intercept with the slope). In this context, the
\(y\)
-intercept is the number of pages Lin read before she starts counting the days (30), and the slope is the number of pages Lin reads per day (40).
Emphasize how the
\(y\)
-intercept and slope influence the graph of a line.
The
\(y\)
-intercept indicates where the line touches or crosses the
\(y\)
-axis.
The slope indicates how steep the line is.


correct_option_index: 0