standard_description: Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
problem_activity: Optional activity
Here students continue to use diagrams to represent sums of decimals, but they also transition to writing addition calculations vertically. They think about the alignment of the digits in vertical calculations to help ensure that correct values are combined. This activity is optional, so students have the option to spend more time subtracting decimals in the next activity.
As in the previous activity, consider having students use physical base-ten blocks (if available), a paper version of the base-ten figures (from the blackline master), or this digital applet
ggbm.at/FXEZD466
, as alternatives to drawing diagrams.
Digital
Launch
Remind students that the term “sum” means the result of an addition. Refer to the image from the previous activity that shows how several squares and rectangles were used to represent base-ten units. Tell students to use the same representations in this activity and to keep in mind that in the process of bundling they find more sums of decimals.
Arrange students in groups of 2. Give students 10 minutes of quiet work time, but encourage them to briefly discuss their responses with their partner after completing the second question and before continuing with the rest. Follow with a whole-class discussion.
Classes using the digital activities have an interactive applet with virtual blocks. In this activity, students must redefine the value of each block to represent the place values in each problem. To use the bundling and unbundling features, the pieces must be aligned on the light blue grids. To bring a piece into the workspace, select one of the green tool icons and then click on the workspace. To move it, you must click on the Move tool (the arrow).
[IMG]
Action and Expression: Develop Expression and Communication.
Use virtual or concrete manipulatives to connect symbols to concrete objects or values. Encourage students to begin with physical representations before drawing a diagram. Provide access to physical or virtual base-ten blocks to support drawing diagrams.
Supports accessibility for: Conceptual processing
Conversing: MLR1 Stronger and Clearer Each Time.
Use this routine to give students an opportunity to refine their explanation about which calculation is correct for
\(0.2 + 0.05\)
. At the appropriate time, give students time to meet with 2–3 partners to share their response. Display prompts students can use to provide feedback such as, “How did the alignment of the decimals change the sum?”, “Why is aligning decimal places important here?” and "A detail (or word) you could add is _____, because . . . ." As students discuss, listen to how they talk about combining units, aligning digits of the same place values, and whether it is necessary to add zeros. Give students 1–2 minutes to revise their writing based on their conversations.​
Design Principle(s): Optimize output (for justification)
Student Facing
Andre and Jada drew base-ten diagrams to represent
\(0.007 + 0.004\)
. Andre drew 11 small rectangles. Jada drew only two figures: a square and a small rectangle.
[IMG]
If both students represented the sum correctly, what value does each small rectangle represent? What value does each square represent?
Draw or describe a diagram that could represent the sum
\(0.008 + 0.07\)
.
Here are two calculations of
\(0.2 + 0.05\)
. Which is correct? Explain why one is correct and the other is incorrect.
[IMG]
Compute each sum. If you get stuck, consider drawing base-ten diagrams to help you.
[IMG]
\(0.209 + 0.01\)
\(10.2 + 1.1456\)
The applet has tools that create each of the base-ten blocks. This time you need to decide the value of each block before you begin.
Select a Block tool, and then click on the screen to place it.
Click on the Move tool (the arrow) when you are done choosing blocks.
Subtract by deleting with the delete tool (the trash can), not by crossing out.
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Print
Launch
Remind students that the term “sum” means the result of an addition. Refer to the image from the previous activity that shows how several squares and rectangles were used to represent base-ten units. Tell students to use the same representations in this activity and to keep in mind that in the process of bundling they find more sums of decimals.
Arrange students in groups of 2. Give students 10 minutes of quiet work time, but encourage them to briefly discuss their responses with their partner after completing the second question and before continuing with the rest. Follow with a whole-class discussion.
[IMG]
Classes using the digital activities have an interactive applet with virtual blocks. In this activity, students must redefine the value of each block to represent the place values in each problem. To use the bundling and unbundling features, the pieces must be aligned on the light blue grids. To bring a piece into the workspace, select one of the green tool icons and then click on the workspace. To move it, you must click on the Move tool
Action and Expression: Develop Expression and Communication.
Use virtual or concrete manipulatives to connect symbols to concrete objects or values. Encourage students to begin with physical representations before drawing a diagram. Provide access to physical or virtual base-ten blocks to support drawing diagrams.
Supports accessibility for: Conceptual processing
Conversing: MLR1 Stronger and Clearer Each Time.
Use this routine to give students an opportunity to refine their explanation about which calculation is correct for
\(0.2 + 0.05\)
. At the appropriate time, give students time to meet with 2–3 partners to share their response. Display prompts students can use to provide feedback such as, “How did the alignment of the decimals change the sum?”, “Why is aligning decimal places important here?” and "A detail (or word) you could add is _____, because . . . ." As students discuss, listen to how they talk about combining units, aligning digits of the same place values, and whether it is necessary to add zeros. Give students 1–2 minutes to revise their writing based on their conversations.​
Design Principle(s): Optimize output (for justification)
Student Facing
Andre and Jada drew base-ten diagrams to represent
\(0.007 + 0.004\)
. Andre drew 11 small rectangles. Jada drew only two figures: a square and a small rectangle.
[IMG]
If both students represented the sum correctly, what value does each small rectangle represent? What value does each square represent?
Draw or describe a diagram that could represent the sum
\(0.008 + 0.07\)
.
Here are two calculations of
\(0.2 + 0.05\)
. Which is correct? Explain why one is correct and the other is incorrect.
[IMG]
Compute each sum. If you get stuck, consider drawing base-ten diagrams to help you.
[IMG]
\(0.209 + 0.01\)
\(10.2 + 1.1456\)
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Activity Synthesis
The goal of this discussion is to help students understand that vertical calculation is an efficient way to find the sums of decimals. Discuss:
“When finding
\(0.008 + 0.07\)
, why do we not combine the 8 thousandths and 7 hundredths to make 15?” (Hundredths and thousandths are different units. If each hundredth is unbundled into 10 thousandths, we can add 70 thousandths and 8 thousandths to get 78 thousandths).
“How do we use representations of base-ten numbers to add effectively and efficiently?” (Make sure to put together tenths with tenths, hundredths with hundredths, etc. Also, make sure that if a large square represents
\(\frac{1}{10}\)
for one summand, it also represents
\(\frac{1}{10}\)
for the other.)
“When adding numbers without using base-ten diagrams or other representations, what can we do to help add them correctly?” (Pay close attention to place value so we combine only like units. It is helpful to line up the digits of the numbers so that numerals that represent the same place value are placed directly on top of one another.)
Additionally, consider using color coding to help students visualize the place-value structure, as shown here.
[IMG]


aligns: no