Scale factors and similar shapes
Enlarge a shape by a scale factor, spot similar shapes, find a scale factor, and draw a similar shape from one side.
- UK: Year 6
- France: grade 8
- Germany: grade 9
- Iran: grade 9
- Afghanistan: grade 8
- Syria: grade 5
- Ukraine: grade 8
- Russia: grade 8
Guide
Two shapes are similar when one is an enlargement of the other: matching angles are equal and every side is multiplied by the same number. That number is the scale factor (ratio of similarity).
The classic mistake at this age is adding instead of multiplying. Adding 2 to each side of a 3 × 1 rectangle gives 5 × 3, which is a different shape: no longer long and thin. To enlarge, multiply every side.
Turning or flipping a shape does not stop it being similar. A scale factor does not have to be a whole number: 1.5 is fine.