1. A proportion is a mathematical statement showing that two ratios are equal. A proportion is written as an equation with a ratio on each side of the equal sign.
Remember to include units when writing a rate. Also, keep in mind that the order of the units is important. Be sure that like units for each rate are in the same position.
Example 1. Write each sentence as a proportion.
Answer:
a) 4 is to 9 as 12 is 27.
b) If 7 ounce is 150 calories, then 14 ounces is 300 calories.
Your Turn Problem #1
Write each sentence as a proportion.
a) 7 is to 3 as 21 is 9.
b) If 4 gallons of paint will cover 360 square feet, then 6 gallons will cover 540 square feet.
Answers:

2. Determining whether two ratios are proportional
A proportion is a mathematical statement showing that two ratios are equivalent.
Sometimes it is not as obvious.
A way of verifying whether two ratios are proportional is by determining whether their cross products are equal.
8 × 21 = 168, and also 12 × 21 = 168
Therefore the ratios are proportional.
Next Slide

3. Example 2. Determine whether the ratios are proportional.
Multiply the cross products. If the answers are identical, then the ratios are proportional.
The ratios are proportional
Your Turn Problem #2
Determine whether the ratios are proportional.
Answer:
The ratios are not proportional
The End
B.R.
6-4-08