Lesson 12
Decimal Game Day
Warmup: True or False: Adding Decimals (10 minutes)
Narrative
The purpose of this True or False is for students to demonstrate strategies and understandings they have for adding decimals. These understandings help students deepen their understanding of the properties of operations and will be helpful later in the lesson when students will need to be able to add decimals.
Launch
 Display one equation.
 “Give me a signal when you know whether the equation is true and can explain how you know.”
 1 minute: quiet think time
Activity
 Share and record answers and strategy.
 Repeat with each equation.
Student Facing
Decide if each statement true or false. Be prepared to explain your reasoning.
 \(0.99 + 0.1 = 0.9 + 0.1 + 0.09\)
 \(0.99 + 0.01 = 0.9 + 0.1\)
 \(0.99 + 0.1 = 1.99\)
Student Response
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Activity Synthesis
 Display the first and third equations.
 “How can you justify your answer without evaluating both sides?” (For the first problem, I noticed that there are 9 tenths on the right and left and also 10 hundredths. For the third problem, I saw that the right hand side is almost 2 so it's much larger than the left hand side.)
Activity 1: Race to One or One Tenth (15 minutes)
Narrative
The purpose of this activity is for students to practice adding decimals. There are two versions of the game, Race to One and Race to One Tenth. Students can choose which version to play, or, if there is time, play both versions of the game. Consider playing a round of the game with students during the launch to demonstrate how it is played.
Advances: Reading, Representing
Supports accessibility for: Memory, Organization
Required Materials
Materials to Gather
Required Preparation
 Each group of 2 needs a number cube.
Launch
 Groups of 2
 “Take a minute to read over the directions for Race to One or Race to One Tenth.”
 1 minute: quiet think time
 “Are there any questions before we get started?”
 Give students a set of cards.
Activity
 “Play Race to One or One Tenth.”
 10–12 minutes: partner work time
Student Facing
Use the directions to play Race to One or One Tenth with your partner. If there is time, play both versions of the game.
Race to One
 Roll the number cube.
 Decide if you want the number to represent tenths or hundredths.
 Add the number to the last sum on your score sheet. If it is your first turn, you will add the number you roll to zero.
 Take turns continuing to roll the number cube, decide the value, and add the number to your previous sum.
 The first player to reach exactly 1 is the winner.
 If you go over one, you lose your turn. For example, if your last sum was .95 and you roll a 6, you cannot go.
 You may not need to use all the blank spaces on your score sheet or you may need to write more spaces.
number rolled  0.1  0.01  equation to represent the total  

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Race to One Tenth
 Roll the number cube.
 Decide if you want the number to represent hundredths or thousandths.
 Add the number to the last sum on your score sheet. If it is your first turn, you will add the number you roll to zero.
 Take turns continuing to roll the number cube, decide the value, and add the number to your previous sum.
 The first player to reach exactly 0.1 is the winner.
 If you go over 0.1, you lose your turn. For example, if your last sum was .095 and you roll a 6, you cannot go.
 You may not need to use all the blank spaces on your score sheet or you may need to write more spaces.
number rolled  0.01  0.001  equation to represent the total  

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Student Response
For access, consult one of our IM Certified Partners.
Activity Synthesis
 “How are the two games, Race to One and Race to One Tenth the same?” (In both cases, I ended up close to the goal value and then had to keep rolling, hoping I got the right number.)
 “How are the games different?” (In Race to One, I am aiming for 1 and in Race to One Tenth I am trying to get 0.1. When I get close to 1 in Race to One I have to choose hundredths and when I get close to 0.1 in Race to One Tenth I have to choose thousandths.)
 “How did you decide whether to have a number represent tenths or hundredths in Race to One?” (If I wasn’t close to one, I would have it represent the larger value.)
Activity 2: Decimal Race to 500 (20 minutes)
Narrative
Required Materials
Materials to Gather
Required Preparation
 Each group of 2 needs a paper clip.
Launch
 Groups of 2
 “Take a minute to read over the directions for Decimal Race to 500.”
 1 minute: quiet think time
 Give students paper clips.
Activity
 “Play Decimal Race to 500 with your partner.”
 10–15 minutes: partner work time
Student Facing

Spin the spinner three times.

Arrange the digits to make a decimal number that follows this rule:

Odd numbers can only be used in the tenths, hundredths, or thousandths place.

Even numbers can only be used in the ones, tens, and hundreds places.
For example, if you spin the numbers 2, 3, and 9, these are some of the possible numbers you could make: 2.39 or 2.93.


Add your number to your previous sum. If it is your first turn, you will add your number to zero.

Continue taking turns until one person has reached 500 or more.
Student Response
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Activity Synthesis
 “What number would you choose to make if you spun 1, 8, and 4? Why?” (84.1 because that’s the biggest number I can make with those digits.)
 “Is it possible to win the game in one turn? How?” (Yes, I can spin 6, 2, and 8 and then can make 862 and that’s the end of the game.)
 “What numbers are the worst numbers to spin if you want to win the game quickly?” (Odd numbers because they only count for tenths, hundredths, or thousandths. Also 0 is no good unless there are some other even numbers.)
 “Can you think of a way to change this game to make it more challenging?” (Make it so you have to land exactly on 500.)
Lesson Synthesis
Lesson Synthesis
“Today, we practiced adding decimals. How is adding and subtracting with decimals the same as adding and subtracting with whole numbers? How is it different?” (If I add digits with the same place value, I can use the same method to add decimals as I use to add whole numbers. I have to make sure to add digits with the same place value so I can't always line up the digits to the right, like I do with whole numbers.)
Cooldown: Reflect on Operating with Decimals (5 minutes)
CoolDown
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