1. Section 7-1: Ratios and Proportions
Chapter 7: Similarity
Section 7-1:
Ratios and Proportions

2. Objectives
To write ratios and solve proportions.

3. Vocabulary Ratio Proportion Extended Proportion Cross-Product Property
Scale Drawing
Scale

4. Ratio A ratio is a comparison of two quantities.
If you are comparing a to b, you may write as a proportion:
Fraction form:_______ (b ≠ 0)
Ratio form: a : b

5. Example
A photo is 8 in. wide and 5 1/3 in high. It is enlarged to a poster that is 2 ft. wide and 1 1/3 ft. high. What is the ratio of the width of the picture to the width of the poster?

6. Proportion A proportion is a statement that two ratios are equal.
You can write a proportion in the following forms:

7. Extended Proportion
When three or more ratios are equal, you can write them as an extended proportion.
Example:

8. Properties of Proportions:

9. Cross-Product Property
The product of the extremes is equal to the product of the means.
Also known as “Cross-Multiplying”

10. Solve the proportion:

11. Solve the proportion:

12. Solve the proportion:

13. Solve the proportion:

14. Solve the proportion:

15. Scale Drawing
A scale drawing is a drawing in which all lengths are proportional to corresponding actual lengths.

16. Scale
A scale is the ratio of any length in a scale drawing to the corresponding actual length.
The lengths may be different units.

17. Geography Example
Students at the University of Minnesota in Minneapolis built a model globe 42 ft. in diameter using a scale of 1: 1,000,000.
About how tall is Mount Everest on the model if it is actually about 29,000 ft tall?