Lesson 14

Find the Area of Figures with Missing Sides

Lesson Purpose

The purpose of this lesson is for students to calculate the area of ungridded figures made of rectangles, including figures with missing side lengths.

Lesson Narrative

In previous lessons, students found the area of figures that were fully gridded with squares and moved toward figures without a grid but had all their side lengths labeled. In this lesson, students use the strategies they have learned to decompose the figures into non-overlapping rectangles. They realize that not all measurements need to be given, and that some lengths can be determined given the rectangular structure of these figures.

  • Engagement
  • MLR8

Learning Goals

Teacher Facing

  • Calculate the area of ungridded figures composed of rectangles, including figures with missing side lengths.

Student Facing

  • Let’s find the area of figures with missing side lengths.

Required Preparation

CCSS Standards


Lesson Timeline

Warm-up 10 min
Activity 1 10 min
Activity 2 25 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

Reflect on which students have not shared their strategies in class lately. How can their insight or ways of thinking be highlighted in or tied to upcoming lessons?

Suggested Centers

  • Five in a Row: Multiplication (3–5), Stage 2: Factors 1–9 (Addressing)
  • Five in a Row: Addition and Subtraction (1–2), Stage 8: Add within 1,000 with Composing (Supporting)

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