Understanding Scale Factor in Geometry - Interactive Lesson

1. scale factor

2. Scale factor is the ratio of change between two sides. The number you multiply by to relate the first shape to the second is the scale factor.

3. If a shape becomes twice as big, the scale factor would be two. If a shape shrinks to half its size, the scale factor is ½. Let’s take a look.

4. Now Look at the BLUE translation and write down the base and height… Take a look at the RED shape, write down the base and height…

5. How many times bigger is the blue shape? 2 is your scale factor because 5 x 2 = 10 and 4 x 2 = 8 What did you get? 5 10 4 8

6. 6 9 2 3 For 6 to become 2, you must multiply by 1/3 and for 9 to become 3 you must also multiply by 1/3. So your scale factor is….1/3 Both 6 and 9 reduce in size by dividing 3 BUT scale factor must be a relation by multiplying. Now take a look at the transformation, what has been the amount of reduction?

7. 2 3 8 12 Both 2 and 3 are multiplied by 4. This means the scale factor is 4. Now take a look at the transformation, what has been the amount of enlargement?

8. What is the scale factor? 5 15 7 21 A B C D 3 1/3 5 10

9. What is the scale factor? 8 16 B A C D 3 2 1/2 8

10. What is the scale factor? 4 12 A B C D 3 1/2 1/3 9

11. What is the scale factor? 3 18 A B C D 9 4 1/6 6

12. A Mustang GT is 16 feet long. A model of it was built with a scale of 1 in : 2 ft. How long is the model. A B C D 9 in 16 in 16 ft 8 in