options: Write and interpret numerical expressions.

Solve problems involving the four operations, and identify and explain patterns in arithmetic.

Reason about and solve one-variable equations and inequalities.

Create equations that describe numbers or relationships

Use properties of operations to generate equivalent expressions.

Interpret the structure of expressions.

Multiply and divide within 100.

Use polynomial identities to solve problems.

Apply and extend previous understandings of arithmetic to algebraic expressions.

Represent and solve problems involving addition and subtraction.

Analyze and solve linear equations and pairs of simultaneous linear equations.

Write expressions in equivalent forms to solve problems.

Work with equal groups of objects to gain foundations for multiplication.

Represent and solve equations and inequalities graphically.

Solve systems of equations.

Generate and analyze patterns.

Represent and analyze quantitative relationships between dependent and independent variables.

Analyze patterns and relationships.

Understand solving equations as a process of reasoning and explain the reasoning.

Understand and apply properties of operations and the relationship between addition and subtraction.

Understand addition as putting together and adding to, and understand subtraction as taking apart and taking from.

Use the four operations with whole numbers to solve problems.

Solve real-life and mathematical problems using numerical and algebraic expressions and equations.

Work with radicals and integer exponents.

Add and subtract within 20.

Understand properties of multiplication and the relationship between multiplication and division.

Represent and solve problems involving multiplication and division.

Rewrite rational expressions.

Understand the connections between proportional relationships, lines, and linear equations.

Perform arithmetic operations on polynomials.

Work with addition and subtraction equations.

Understand the relationship between zeros and factors of polynomials.

Gain familiarity with factors and multiples.

Solve equations and inequalities in one variable.
problem_activity: Activity
In this activity, students practice constructing an exponential function and evaluating it at a fractional input value as they translate between decades and years. They also think about how to express a percent increase over a fractional interval of input—specifically, how to express the annual growth rate of a population given the growth rate for one decade. They analyze and articulate why the growth rate for one year is
not
one tenth of that of one decade (MP3).
Launch
Tell students that, as of 2017, Nigeria is the seventh-most populous country in the world. It has grown at a fairly steady (and relatively high) rate since 1980.
Speaking, Reading: MLR5 Co-Craft Questions.
Use this routine to orient students to the language of exponential functions in context. Ask students to keep their books or devices closed, and display only the image of the map and the problem statement, without revealing the questions that follow. Arrange students in groups of 2, and invite them to create a list of mathematical questions that could be asked about the situation.  Listen for and amplify questions about growth and decay factors, percent increase or decrease, fractional intervals, and comparisons of growth rates. Invite 2–3 groups to share their questions with the class.
Design Principle(s): Maximize meta-awareness; Support sense-making
Student Facing
[IMG]
In 1990, Nigeria had a population of about 95.3 million. By 2000, there were about 122.4 million people, an increase of about 28.4%. During that decade, the population can be reasonably modeled by an exponential function.
Express the population of Nigeria
\(f(d)\)
, in millions of people,
\(d\)
decades since 1990.
Write an expression to represent the population of Nigeria in 1996.
A student said, “The population of Nigeria grew at a rate of 2.84% every year.”
Explain or show why the student’s statement is incorrect.
Find the correct annual growth rate. Explain or show your reasoning.
Student Response
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Anticipated Misconceptions
If students struggle to identify the input to their function where
\(d\)
is not an integer, remind them that there are 10 years in a decade. Then ask them how many decades is 6 years? What about one year?
Activity Synthesis
Focus the discussion on why the annual growth rate is not
\(\frac1{10}\)
of 28.4%. Consider asking students:
“Why might someone think the annual population growth rate is 2.84%?” (Because 28.4 divided by 10 is 2.84, and they assume that population was growing linearly, or by the same amount each year, rather than by the same factor each year.)
“How can we determine the growth factor for one year?” (We know that when the annual growth factor, say
\(b\)
, is raised to an exponent of 10, it must equal 1.284, or
\(b^{10} = 1.284\)
, so
\(b\)
must be
\(1.284^\frac{1}{10}\)
or
\(\sqrt[10]{1.284}\)
because raising that number to an exponent of 10 gives 1.284.)
“How do we express the factor as a growth rate? (
\(1.284^\frac{1}{10} \approx 1.0258\)
, so the growth rate is 2.58%.)
Representation: Internalize Comprehension.
Use color and annotations to illustrate student thinking. As students share their reasoning about the last question, scribe their thinking on a visible display. To illustrate why the growth factor for one year is not
\(\frac{1}{10}\)
of that of a decade, it may be helpful to return to a diagram that is configured like a double number line (especially if used in the last lesson). Use the double number line of years and decades to annotate and show the growth factor. When students explain that the growth factor for one decade is 1.284, draw an arrow across the decade line and label it
\(\boldcdot 1.284\)
. Then draw small arrows for the years labeled with
\(\boldcdot b\)
for each segment. Label the decade line with the corresponding equation. Encourage students to refer to the diagram when explaining why
\(b\)
is not one-tenth the growth rate of a decade. When students first explain the use of the fractional exponent to calculate the yearly population growth, label the line representing years with the corresponding equation.
Supports accessibility for: Visual-spatial processing; Conceptual processing


correct_option_index: 5