Lesson 3
Thousandths in Expanded Form
Warmup: Which One Doesn't Belong: Different Ways to Express a Decimal Number (10 minutes)
Narrative
This warmup prompts students to compare four expressions. The particular expressions chosen give students a chance to focus on several important features, including:
 the operations
 the values of the expressions
 the types of numbers in the expressions (whole numbers versus decimals)
Students work in this lesson to express decimals in many different forms, and this warmup gives students some familiarity thinking about some of those different forms.
Launch
 Groups of 2
 Display the image.
 “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
 1 minute: quiet think time
Activity
 “Discuss your thinking with your partner.”
 2–3 minutes: partner discussion
 Share and record responses.
Student Facing
Which one doesn't belong?
 \(26\div100\)
 \(0.26\)
 \(26 \times 0.001\)
 \((2 \times 0.1) + (6 \times 0.01)\)
Student Response
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Activity Synthesis
 Display the expression: \(2 \times 0.1 + 6 \times 0.01\)
 “How is this expression different from the others?” (It is written as a sum. The different place values are written separately.)
 “Today we are going to represent decimal numbers in this way.”
Activity 1: Expanded Form (20 minutes)
Narrative
Launch
 Groups of 2
Activity
 15 minutes: partner work time
Student Facing

 Explain or show why the shaded region represents \((4 \times 0.1) + (1 \times 0.01) + (9 \times 0.001)\).
 What decimal number represents the shaded region?
 Explain or show why the shaded region represents \((4 \times 0.1) + (1 \times 0.01) + (9 \times 0.001)\).

 Shade the grid to represent \((8 \times 0.1) + (3 \times 0.01) + (5 \times 0.001)\).
 Write the number \((8 \times 0.1) + (3 \times 0.01) + (5 \times 0.001)\) in decimal form.
 Mai says that the decimal 0.105 represents \((1 \times 0.1) + (5 \times 0.01)\). Do you agree with Mai? Explain or show your reasoning.
Student Response
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Activity Synthesis
 Display the diagram from the student workbook that shows \(0.835\).
 Consider circling each part of the diagram as students respond to the questions.
 “What part of the diagram shows \(8 \times 0.1\)? How do you know?” (The 8 shaded horizontal strips because they are each tenths or 0.1.)
 “What part of the diagram shows \(3 \times 0.01\)? How do you know?” (The 3 single shaded squares because they are hundredths or 0.01.)
 “What part of the diagram shows \(5 \times 0.001\)? How do you know?” (The 5 tiny shaded pieces because they are each thousandths or 0.001.)
 “What does the 5 in 0.105 represent?” (5 thousandths)
 “I can write 0.105 as \(1 \times 0.1 + 5 \times 0.001\) to show that it is 1 tenth and 5 thousandths. This is called the expanded form of a decimal.”
Activity 2: Decimal Numbers in Numerous Ways (15 minutes)
Narrative
The purpose of this activity is for students to practice different ways of expressing decimal numbers to the thousandth. In addition to standard decimal digit form, these ways include:
 diagrams
 expanded form
 fractions
 words
Launch
 Groups of 2
 Display the first image that represents the number 0.742 in the student workbook.
 “What are some different ways we can represent the number shown in the diagram?”
 0.742
 seven hundred fortytwo thousandths
 \(0.7 + 0.04 + 0.002\)
 \((7\times 0.1)+(4 \times 0.01)+(2\times 0.001)\)
 \(\frac {742}{1,000}\)
 1 minute: quiet think time
 Share and record responses.
Activity
 “Now find as many ways as you can to represent each number.”
 2 minutes: independent work time
 6 minutes: partner work time
Student Facing
Represent each number in as many ways as you can.


\(\frac{477}{1,000}\)
 one hundred thirtysix thousandths

\((3 \times 0.1) + (6 \times 0.01) + (8 \times 0.001)\)
Student Response
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Advancing Student Thinking
Activity Synthesis
 Invite students to share their representations of \(\left(3 \times 0.1\right) + \left(6 \times 0.01\right) + \left(8 \times 0.001\right)\).
 Display: 0.368
 “How does each digit in the decimal relate to the expanded form?” (The 3 is 3 groups of 1 tenth or 0.3, the 6 is six groups of 1 hundredths or 0.06, and the 8 is 8 groups of 1 thousandth or 0.008.)
 Display: \(\frac{368}{1,\!000}\)
 “How does the expanded form relate to the fraction?” (The 300 is the 3 tenths, the 60 is the 6 hundredths, and the 8 is the 8 thousandths.)
 Display student work that shows 0.368 represented on the hundredths grid.
 “How does the expanded form relate to the diagram?” (The 3 tenths are the top 3 rows. The 6 hundredths are the 6 squares in the next row. The 8 thousandths are the small rectangles.)
Lesson Synthesis
Lesson Synthesis
“Today we represented decimal numbers in many ways.”
Display: 0.315
“What are some different ways you can represent this number? What is your favorite way?” (Three hundred fifteen thousandths, \(\frac {315}{1,000}\) , \((3 \times 0.1) + (1 \times 0.01) + (5 \times 0.001)\), or I could draw a diagram. My favorite way is the decimal because it's the shortest.)
Display responses for all to see.
Cooldown: Different Ways to Write a Decimal Number (5 minutes)
CoolDown
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