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Round and Round Again

Grade 3: Unit 3: Lesson 16

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Let’s look for patterns in rounding.

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Number Talk: More Groups, Fewer Groups

Warm-Up

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Find the value of each expression mentally.

5 x 7

b. 4 x 7

c. 6 x 7

b. 4 x 8

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Let’s Talk About It!

How does knowing 5 x 7 help you find some of the other products?

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All the Numbers

Activity 1

MLR 8: Discussion Supports

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a. What are all the numbers that would round to 50 if you’re rounding to the nearest ten? You can use this number line if it helps you.

b. What are all the numbers that would round to 70 if you’re rounding to the nearest ten?�

c. What are all the numbers that would round to 600 if you’re rounding to the nearest hundred?

Launch

• Groups of 2

• “Diego is thinking of a number. When you round Diego’s number to the nearest ten, the answer

is 40. What’s a number that could be Diego’s number? What’s a number that could not be

Diego’s number?” (38 rounds to 40 so it could be his number. 34 does not round to 40 so it

couldn’t be his number.)

• 30 seconds: quiet think time

• Share 3–5 responses. Highlight the idea that more than one number can round to 40 and that

some numbers are greater than 40 and some are less than 40.

Student Work Time

• “Work with your partner on all these problems. Be sure to justify your reasoning.”

• 5–7 minutes: partner work time

If you finish early, find the numbers that would round to 100 and to 500 if you’re rounding to the

nearest hundred. Compare your lists with a partner’s lists and discuss patterns you see.

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Let’s Talk About It!

How did you decide what numbers would round to 40?

Look at your responses for the first 2 problems. What patterns do you see in the numbers? Why is that happening?

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What’s My Mystery Number?

Activity 1

Action and Expression

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Write down a number between 100 and 1,000 on your index card.

This is your mystery number.

Fold your index card in half so that no one can see your mystery number.

Launch

• Groups of 4

• “We’re going to play a game in which you have to guess a mystery number that someone in

your group writes down.”

• Choose a mystery number and give the class three clues. Play a round of the game with the

class and discuss the clues. Consider using 275 and these clues:

◦ “My mystery number is odd.”

◦ “My mystery number rounds to 300.”

◦ “My mystery number is between 270 and 278.”

• “You’ll give your group three clues by finishing three sentences. The first clue should tell

whether the number is even or odd. Take a couple minutes to choose a mystery number and

write down your three clues.”

• 2 minutes: independent work time

Student Work time

• “Now, you’re going to play the game with your group. Everyone will get a chance to share the

clues for their mystery number. If you have time, you can each create a new mystery number

with three new clues.”

• 12–15 minutes: small-group work time

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Write down 3 clues about your mystery number by finishing these sentences:

1. My mystery number is (odd or even) _____.

2. My mystery number rounds to _____.

3. My mystery number is between _____ and _____.

Launch

• Groups of 4

• “We’re going to play a game in which you have to guess a mystery number that someone in

your group writes down.”

• Choose a mystery number and give the class three clues. Play a round of the game with the

class and discuss the clues. Consider using 275 and these clues:

◦ “My mystery number is odd.”

◦ “My mystery number rounds to 300.”

◦ “My mystery number is between 270 and 278.”

• “You’ll give your group three clues by finishing three sentences. The first clue should tell

whether the number is even or odd. Take a couple minutes to choose a mystery number and

write down your three clues.”

• 2 minutes: independent work time

Student Work time

• “Now, you’re going to play the game with your group. Everyone will get a chance to share the

clues for their mystery number. If you have time, you can each create a new mystery number

with three new clues.”

• 12–15 minutes: small-group work time

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Play What’s My Number?

1. Read the clues for your mystery number.�

2. Starting with the person on your right, have every member in your team try to guess your

mystery number and explain their reasoning.�

3. If they haven’t guessed the mystery number by the time the last person shares, reveal the

mystery number.�

4. Repeat steps 1 through 3 with the next person in the group reading the clues for their mystery

number.

Launch

• Groups of 4

• “We’re going to play a game in which you have to guess a mystery number that someone in

your group writes down.”

• Choose a mystery number and give the class three clues. Play a round of the game with the

class and discuss the clues. Consider using 275 and these clues:

◦ “My mystery number is odd.”

◦ “My mystery number rounds to 300.”

◦ “My mystery number is between 270 and 278.”

• “You’ll give your group three clues by finishing three sentences. The first clue should tell

whether the number is even or odd. Take a couple minutes to choose a mystery number and

write down your three clues.”

• 2 minutes: independent work time

Student Work time

• “Now, you’re going to play the game with your group. Everyone will get a chance to share the

clues for their mystery number. If you have time, you can each create a new mystery number

with three new clues.”

• 12–15 minutes: small-group work time

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Let’s Talk About It!

As you played the game, what clues were the most helpful and why?

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Lesson Synthesis

In the last few lessons we learned about rounding to the nearest ten and hundred. What are some important things you have found helpful to remember when you are rounding?

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What is Clare’s Mystery Number?

Cool-Down

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Clare says she’s thinking of a mystery number and gives these three clues:

• The number is even.

• The number rounded to the nearest ten is 270.

• The number is between 260 and 280.

What are 2 numbers that could be Clare’s mystery number?

Cool-Down: What is Clare’s Mystery Number?

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Image Citations

https://giphy.com/gifs/letters-numbers-shurly-3o6Zt7yXxGpZSY6mgU

https://cutewallpaper.org/download.php?file=/24/child-talking-clipart/114195401.jpg

https://pixabay.com/vectors/magnifying-glass-magnify-glass-1293096/

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