Lesson 6

Compare Decimals on the Number Line

Warm-up: Notice and Wonder: Nested Lines (10 minutes)

Narrative

The purpose of this Notice and Wonder is for students to look at different number lines that all start at 0 but show different decimals. The number lines are nested, that is each successive one is contained in the previous one. The key points for students to notice are that the number lines all have decimals on them and that the size of those decimals is getting smaller. In the lesson, they will plot decimals on number lines like these.

Launch

• Groups of 2
• Display the image.
• “What do you notice? What do you wonder?”
• 1 minute: quiet think time

Activity

• 1 minute: partner discussion
• Share and record responses.

Student Facing

What do you notice? What do you wonder?

Student Response

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Activity Synthesis

• “What are the tick marks on the top number line?” (one tenth, two tenths, three tenths, and so on)
• “Today we are going to use number lines like these to locate different decimals.”

Activity 1: Locate 1 Thousandth (15 minutes)

Narrative

The purpose of this activity is for students to plot the same number on different number lines and recognize that the location of the number on the number line can only be accurately determined when it lies on a tick mark. As they work on locating the number, students reinforce their understanding of place value as the tick marks on the number lines are tenths, hundredths, and thousandths (MP7). Students may struggle to locate 0.001 on the first two number lines. The important take-away is that when a decimal does not lie on a tick mark estimation is needed to locate the number and it can be difficult or impossible to locate it precisely (MP6).

MLR8 Discussion Supports. Prior to solving the problems, invite students to make sense of the situations. Monitor and clarify any questions about the context.
Engagement: Provide Access by Recruiting Interest. Provide choice. Invite students to decide which number line to label first.
Supports accessibility for: Attention, Organization

• Groups of 2

Activity

• 5 minutes: independent work time
• 5 minutes: partner discussion
• Monitor for students who reason about place value to:
• label each tick mark
• locate 0.001 on each number line

Student Facing

On each number line:
• Label all of the tick marks.
• Locate and label the number 0.001.

Student Response

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Activity Synthesis

• Ask previously identified students to share.
• “How did you decide what to label the tick marks on the first number line?” (There are ten tick marks and there are ten tenths in one whole so I counted by tenths.)
• “Where is ten tenths on the first number line?” (The number 1 is ten tenths.)
• “How did you decide what to label the tick marks on the second and third number lines?” (There are 10 hundredths in 1 tenth. There are ten thousandths in 1 hundredth.)
• “How was locating 0.001 different for each of the number lines?” (It was so close to 0 on the first number line that I could not plot it. I could estimate its location on the second number line and then it was the first tick mark on the last number line.)

Activity 2: Label and Compare Decimals (10 minutes)

Narrative

The purpose of this activity is for students to label number lines where the end tick marks are tenths or hundredths written as decimals. They will use their understanding of place value when they label the tick marks (MP7). Students also choose one of the number lines to compare two numbers, preparing them for the comparison work in the next activity and in future lessons.

• Groups of 2

Activity

• 4–5 minutes: independent work
• 2–3 minutes minutes: partner discussion
• Monitor for students who accurately label the number lines with hundredths and thousandths.

Student Facing

1. Label the tick marks on each number line.

2. Which of the number lines would you use to compare 0.534 and 0.537? Explain or show your reasoning.

Student Response

For access, consult one of our IM Certified Partners.

Activity Synthesis

• Ask previously identified students to share their solutions and reasoning.
• “Which number line would you choose to compare 0.534 and 0.537?” (I liked the middle one because those numbers were labeled tick marks and I could see which one was further to the right.)
• “Which number is greater, 0.534 or 0.537? Why?” (0.537 because it is further to the right on the number line.)
• Display inequality: $$0.534 < 0.537$$
• “We can also say that 0.534 is less than 0.537 with symbols.”

Activity 3: Locate and Compare With Symbols (10 minutes)

Narrative

The purpose of this activity is for students to compare decimal numbers using the number line for support. All of the numbers lie on tick marks and students will use their understanding of place value to accurately place the decimals. They will also use their understanding that one number is greater than another when it lies farther to the right on the number line.

• Groups of 2

Activity

• 5 minutes: independent work
• 2 minutes: partner discussion

Student Facing

1. Use the symbol < or > to compare the decimals 0.2 and 0.02. Use the number line to explain or show your thinking.

2. Use the symbol < or > to compare the decimals 0.3 and 0.14. Use the number line to explain or show your thinking.

3. Use the symbol < or > to compare the decimals 0.23 and 0.216. Use the number line to explain or show your thinking.

Student Response

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Activity Synthesis

• “How do number lines help compare decimals?” (We can put the decimals exactly on tick marks and then see which number is farther to the right.)

Lesson Synthesis

Lesson Synthesis

“Today we used place value reasoning to locate and compare decimals to the thousandths place using number lines.”

Display the last number line from the last activity.

”What number is located at the first tick mark after 0.23?” (0.231)

“What number is located at the last tick mark before 0.22?” (0.219)

Label the numbers as students respond.

“Which number is greater? How do you know?” (0.231 because it is farther to the right on the number line)

Cool-down: Locate, Label, and Compare Numbers (5 minutes)

Cool-Down

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