Lesson 12

Estimate and Add

Lesson Purpose

The purpose of this lesson is for students to estimate and find the value of addition expressions with decimals.

Lesson Narrative

In a previous lesson, students found decimal sums in a way that made sense to them. In this lesson, students see that the standard algorithm for whole number addition, familiar from a previous course, also works for decimals. Students then estimate sums and find their values. Students are not required to use the standard algorithm, but see how it is an efficient way to add. 

Display the Decimal Addition chart from a previous lesson to be used during the lesson synthesis.
  • Representation

Learning Goals

Teacher Facing

  • Add decimals to the hundredths place using strategies based on place value.

Student Facing

  • Let’s add decimals and think about whether our answers are reasonable.

Required Preparation

CCSS Standards


Lesson Timeline

Warm-up 10 min
Activity 1 15 min
Activity 2 20 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

What did you say, do, or ask during the lesson synthesis that helped students be clear on the learning of the day? How did understanding the cool-down of the lesson before you started teaching today help you synthesize that learning?

Suggested Centers

  • Tic Tac Round (3–5), Stage 3: Decimals (Addressing)
  • Greatest of Them All (1–5), Stage 4: Decimals (Addressing)
  • Jump the Line (2–5), Stage 2: Add and Subtract Tenths and Hundredths (Supporting)

Print Formatted Materials

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Additional Resources

Google Slides

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PowerPoint Slides

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