Lesson 3.4: Find Percent Change and Percent Error

Lesson 3.4

Solve Percent Change and Percent Error Problems

Definitions:

Percent Change: Describes how much a quantity has changed when compared to its original value. It can be an increase or a decrease. This can also be expressed as percent markup when talking about costs of items.

Percent Error: Describes the accuracy of a measured or accurate value when compared to an actual value. It will always be a positive value.

​Formulas:

​Percent Change:

Amount of Change = Percent Change X Original Amount
Markup = Percent markup X Original Cost

or

New - Old = Percent Change

Old
Percent Error:

Difference in Amount= Percent Error X Actual Amount

​Data reports that 3,000 people attended an event. Upon closer inspection you discover that 3,296 people attended the event. Calculate the percent error.

Difference in Attendance = Percent Error X Actual Attendance

​Find Percent Error:

​The original quantity is 10, the new quantity is 13. What is the percent change? Is it an increase or a decrease?

Multiple Choice

The original quantity is 12 the new quantity is 15. What is the percent change?

• 0.25%

• 25%

• -0.25%

• -25%

Multiple Choice

Originally it appears that 100 kids are in your class. Upon further inspection you discover 120 kids are in your class. What is the percent error?

• 0.2%

• 20%

• 0.167%

• 16.7%

​Liya's team won 8 games last month and 10 games this month. What was the percent change? Was it an increase or a decrease?

Multiple Choice

The RMS sports teams won 35 games last year and 50 games this year. What was the percent change?

• 0.43%

• 43%

• 0.3%

• 30%

You see a shirt that is on sale for 25% off. If the shirt originally cost $40, what is the price of the shirt when it is on sale?

Multiple Choice

You see a shirt that is on sale for 20% off. If the shirt originally cost $50, what is the price of the shirt when it is on sale?

• $50

• $10

• $60

• $40

​Conclusion: Write two complete sentences about what you learned.