Cogito
Grade 7 Math · Chapter 1 · Lesson 1
Scale Copies
The same shape, a different size.
8 problems · about 17 minutes · 7.G.A.1
What this lesson teaches
The child identifies scale copies and finds the scale factor between them.
- A scale copy multiplies every length by the same factor.
- Angles stay exactly the same.
- A factor under 1 shrinks and still counts as a scale copy.
Warm Up
Straightforward practice. Get the method working first.
4 problemsA 9 cm side becomes 27 cm. What is the scale factor?
Answer 3
Why 3.
What makes a copy a scale copy?
Answer Every length multiplied by the same factor.
Why One factor applied to every length.
A 7 cm side scaled by 3. How long is the copy?
Answer 21
Why 7 × 3.
A 6 cm side becomes 18 cm. What is the scale factor?
Answer 3
Why 18 ÷ 6.
Build It Up
The same ideas with more to keep track of.
2 problemsA 20 cm side scaled by 1/2. How long is the copy?
Answer 10
Why Half of 20.
Do angles change when a shape is scaled?
Answer No.
Why Only lengths change.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Photo: A 5 cm side is scaled by 4. How long is the copy?
Answer 20 cm
Why 20 cm.
The Map: A 12 cm side becomes 3 cm. What is the scale factor, as a bottom number of a fraction with top 1?
Answer 4
Why A scale factor of 1/4.