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Composite Figures and Scale Drawings
Students decompose composite figures and apply scale factors to lengths, perimeters, and areas.
Find It. Learn It. Master It.
At a Glance
How can a complex region be reorganized into simpler measurable parts?
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.
4,327 = 4,000 + 300 + 20 + 7
Learning Targets
- Decompose into known shapes.
- Find missing dimensions first.
- Add or subtract areas.
- Lengths scale by k.
- Areas scale by k squared.
Interactive Vocabulary
Add a student-friendly definition in the Binder Page editor.
Add a student-friendly definition in the Binder Page editor.
Add a student-friendly definition in the Binder Page editor.
Worked Examples
L-shaped region
Enclose it in a 10×8 rectangle and subtract a 4×3 cutout.
A=80−12=68 square units.
Rectangle plus semicircle
Add rectangle area and half a circle’s area.
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.
Common Misconceptions
Double-counting overlapping regions
Mark each nonoverlapping part.
Subtracting an unlabeled length incorrectly
Use aligned total lengths to infer it.
Watch, pause, and explain
Use the chapter markers, key vocabulary, and reflection prompts to stay actively engaged while you watch.
Practice until you can explain it
Move from a quick warm-up to guided practice, independent work, and deeper challenges.
Warm-Up
A 12×9 rectangle has a 4×3 corner removed. Find area.
Guided Practice
Two nonoverlapping rectangles 8x5 and 3x4: total A=52.
15x10 rectangle minus 5x4 cutout: A=130.
Scale factor 3, original area 12: new area=108.
Map scale 1 cm:5 km, distance 7 cm: 35 km.
Scale factor 1/2, original perimeter 30: new perimeter=15.
Independent Practice
A 12×9 rectangle has a 4×3 corner removed. Find area.
Create and solve a second example with different values.
Challenge & Real-World Practice
Design a composite figure with total area 150 square units. Provide two valid solution methods and compare their efficiency.
Nice work!
You completed the Practice It learning path.
IXL
Area of Compound Figures
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DeltaMath: Composite Area
Open resourceDeltaMath: Scale Drawings and Area
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