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Composite Figures and Scale Drawings

Students decompose composite figures and apply scale factors to lengths, perimeters, and areas.

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Beginner 15–20 minutes Volume & Area
Volume & Area Page 4 of 8
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At a Glance

Composite Figures and Scale Drawings
Binder SectionVolume & Area
DifficultyBeginner
Estimated Time15–20 minutes
PrerequisitesNone
Essential Question

How can a complex region be reorganized into simpler measurable parts?

Build Understanding

A composite figure combines familiar shapes. Draw helpful boundaries, find missing dimensions, calculate each component, and add or subtract without double-counting.

A scale factor k multiplies every length. Perimeter changes by k, but area changes by k squared. Use the scale statement consistently and include units.

Visual Model
4Thousands 3Hundreds 2Tens 7Ones

4,327 = 4,000 + 300 + 20 + 7

Goals

Learning Targets

  • Decompose into known shapes.
  • Find missing dimensions first.
  • Add or subtract areas.
  • Lengths scale by k.
  • Areas scale by k squared.
Click each word

Interactive Vocabulary

Reveal one step at a time

Worked Examples

Example 1

L-shaped region

1

Enclose it in a 10×8 rectangle and subtract a 4×3 cutout.

Example 2

Rectangle plus semicircle

1

Add rectangle area and half a circle’s area.

Ask and explain

Common Questions

Does area use the same scale factor as length? No, it uses k squared.
Can I split a figure in different ways? Yes, if pieces cover it exactly once.
Should a removed region be added? No, subtract it.
Notice and correct

Common Misconceptions

Double-counting overlapping regions

Mark each nonoverlapping part.

Subtracting an unlabeled length incorrectly

Use aligned total lengths to infer it.

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Warm-Up Guided Independent Challenge
1
Quick Start

Warm-Up

Warm-up 1

A 12×9 rectangle has a 4×3 corner removed. Find area.

2
We Do

Guided Practice

Guided 1

Two nonoverlapping rectangles 8x5 and 3x4: total A=52.

Guided 2

15x10 rectangle minus 5x4 cutout: A=130.

Guided 3

Scale factor 3, original area 12: new area=108.

Guided 4

Map scale 1 cm:5 km, distance 7 cm: 35 km.

Guided 5

Scale factor 1/2, original perimeter 30: new perimeter=15.

3
You Do

Independent Practice

Independent 1

A 12×9 rectangle has a 4×3 corner removed. Find area.

Independent 2

Create and solve a second example with different values.

4
Stretch Your Thinking

Challenge & Real-World Practice

🧩 Challenge

Design a composite figure with total area 150 square units. Provide two valid solution methods and compare their efficiency.

IXL

Khan Academy

DeltaMath

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Success Criteria

Before you begin, I can…

  • I can identify the important information.
  • I can use accurate notation, labels, and units.
  • I can justify and verify my conclusion.
1
Question 1

What should happen before calculating?

2
Question 2

Which response gives the strongest evidence?

3
Question 3

What is an effective accuracy check?

4
Question 4

Why are units or labels important?

5
Question 5

What should a student do after finding an error?

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