1. Proportional Relationships
Lesson 13: Percent of Change

2. Vocabulary
Percent Error: The ratio describing how far an estimate is from the actual amount.

3. Percent of Error Formula
Amount of Error = % of Error
Actual Amount
To find the amount of error, subtract the actual amount and the estimate.
To solve a proportion, cross multiply and divide.

4. Percent Error Examples
Leo estimates that a package weighs 24 pounds. The actual weight is 20 pounds. What is the percent error of his estimate?
Mrs. Davidson had a jar of skittles. A student estimated that there were 238 skittles in the jar. The jar actually had 319 skittles. What is the percent error of the student’s estimate?

5. Vocabulary
Percent of Change: The ratio that compares the amount of change to the original amount.
Percent Increase: The original amount increases causing a positive percent of change.
Percent Decrease: The original amount decreases causing a negative percent of change.

6. Percent of Change Proportion
Amount of Change = % of Change
Original Amount
To find the amount of change, subtract the final amount and the original amount.
To solve a proportion, cross multiply and divide.

7. Percent of Change Examples
Originally a TV is $ On Black Friday it will be $ What is the percent of change?
The sign says 40% off. (percent decrease) What is the original price if the item is $35 on sale?
The original price was$17. I saved $5. What was the percent of change?