Make Sense of Decimal Addition

10 min

Narrative

The purpose of this How Many Do You See? is for students to group common decimal values and compose new units when they describe the images they see. This helps prepare students to add decimals given in numerical form in the lesson. Students may use words, fractions, or decimals to describe how many they see. 

Launch

  • Groups of 2
  • “How many do you see? How do you see them?”  
  • Display the image.
  • 1 minute: quiet think time
Teacher Instructions
  • Display the image. 
  • “Discuss your thinking with your partner.”
  • 1 minute: partner discussion
  • Record responses.
  • Repeat for each image.

Student Task

How many do you see? How do you see them?

Two diagrams. Each squares. Length and width, 1. Each partitioned into 10 rows of 10 of the same size squares. On left, 30 squares shaded. On right, 20 squares shaded. 

<p>Two diagrams. Each squares. Length and width, 1.</p>
Two diagrams. Each squares. Length and width, 1. Each partitioned into 10 rows of 10 of the same size squares. On left, 20 squares shaded. On right, 90 squares shaded. 

Two diagrams. Each squares. Length and width, 1.
Two diagrams. Each squares. Length and width, 1. Each partitioned into 10 rows of 10 of the same size squares. On left, 95 squares shaded. On right, 7 squares shaded. 

Two diagrams. Each squares. Length and width, 1
Two diagrams. Each squares. Length and width, 1. Each partitioned into 10 rows of 10 of the same size squares. On left, 20 squares shaded. On right, 9 squares shaded. 

Sample Response

Sample responses:

  • 0.5: 0.3 and 0.2
  • 1.1: 0.9 and 0.2
  • 1.02: 0.95 and 0.07
  • 0.29: 0.2 and 0.09
Activity Synthesis (Teacher Notes)
  • Display the third image.
  • “How many do you see? How do you see them?” (I see 95 hundredths and 7 hundredths more. I can move 5 hundredths from the second square to the first and then I have 1 full square and 2 more hundredths.)
Standards
Building Toward
  • 5.NBT.7·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.
  • 5.NBT.B.7·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.

15 min

20 min