1. Proportions and Ratios
by Kylan Parayao

2. Vocabulary and Examples
Ratio: A comparison of two numbers or quantities
Numerical Example: 1 apple : 3 oranges
This ratio compares apples to oranges. It means for every apple there are 3 oranges.
Algebraic Example: A/B
Proportions: Is an algebra equation that states two ratios are equal
Numerical Example: 1/2 = 2/4
2 * 2 = 1 * 4
4 = 4
Algebraic Example: 1/2 = x/6
x * 2 = 1 * 6
2x = 6
x = 3

3. Vocabulary and Examples continued
Extremes: the numbers that are located on the top left and the bottom right of the equation.
Means: the numbers that are located on the top right and the bottom left.
Source:

4. Necessary Prior Knowledge
Cross products property
Cross Products is a method of checking proportions to see if the the two ratios are equal, which would make the sentence correct.
For Example: 4 feet/8 people = 12 feet/p people.
Source:

5. Main Ideas
A proportion is a comparison of two ratios that are often in fraction form.
A ratio is a comparison between two values.
Cross products are a method of checking to see if the two proportions are equal.

6. Formulas and examples Ratio: A:B or A/B 1 apple: 3 oranges
Proportion:
A/B = C/D
1/2 = x/6
Cross Products:
A*D = B*C

7. Example Problems Problem 1
Jane has a box of apples and oranges in the ratio of 2:3. If she has six apples, how many oranges does she have?
Problem 2
Solve for x:
x students/6 teachers = 209 students/11 teachers

8. Answers
Problem 1
Jane has a box of apples and oranges in the ratio of 2:3. If she has six apples, how many oranges does she have?
Answer: 2 apples/3 oranges = 6 apples/x oranges
2*x = 6*3; 2x = 18; x = 9
9 oranges
Problem 2
Solve for x:
x students/6 teachers = 209 students/11 teachers
Answer: x*11 = 209*6; 11x = 1254; x = 114
114 students

9. References Class Notes: Unit 2, Concept:Proportions Date:9/22/12
Internet Resources: