2.10 Change Expressed as a Percent

I can find percent change and find the relative error in linear and nonlinear

measurements.

Percent ChangeExpresses an amount of change as a percent

of an original amount.If a new amount is greater, the change is a

percent increase.If a new amount is less, it is a percent

decrease.Ratio of the amount of change to the original

amount

Finding a Percent ChangeA coat is on sale for $74.50. The original

price was $82. what is the discount expressed as a percent change?

This is a percent decrease.

≈0.09, or 9% decrease

You Try!A store buys an electric guitar for $295 and

marks up the price to $340. What is the markup expressed as a percent change?

≈15%

Relative ErrorRatio of the absolute value of the difference

of a measured (or estimated) value and an actual value compared to the actual value.

When expressed as a percent, it is called percent error.

PracticeA decorator estimates that a rectangular rug

is 5 ft by 8 ft, but it is actually 4 ft by 8 ft. Find the percent error.

25%

Minimum and Maximum DimensionsOften, actual measurements are not known.You cannot always be completely accurate.

Think about measuring with a ruler. Precision is limited and sometimes you have to round.

The most any measurement can be off is by half of the unit used to measure.

ExampleYou measure the length of a poster to be 18.5

in to the nearest half inch. What are the minimum and maximum possible lengths of the poster?

You measured to the nearest half inch, so the greatest possible error is 0.25 in (half of your units) in either direction.

Greatest Possible Percent ErrorThe dimensions of a gift box are shown to the

nearest inch. What is the greatest possible percent error in calculating the box’s volume?

What do we know?Greatest possible error is 0.5 inV = lwh

What are we looking for?Solve

ContinuedFind differences for minimum and maximum

volumes.

Use greater difference for greatest possible percent error

AssignmentODDS ONLYP.148 #7-23