Chapter 3: Solving Equations

3.7Percent of Change

Percent of Change

• Percent of Increase– When a value increases from its original amount

• Percent of Decrease– When a value decreases from its original amount

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Example 1

• The price of a sweater decreased from $29.99 to $24.49. Find the percent of decrease.

Example 1a

• Find the percent of change if the price of a CD increases from $12.99 to $13.99. Round to the nearest percent.

Example 1b

• Find the percent of change if the CD is on sale, and its price decreases from $13.99 to $12.99. Round to the nearest percent.

Example 2

• In 1990, there were 1330 registered alpacas in the US. By the summer of 2000, there were 29,856. What was the percent of increase in registered alpacas?

Example 2a

• The number of alpaca owners increased from 146 in 1991 to 2919 in 2000. Find the percent of increase. Round to the nearest percent.

Greatest Possible Error

• One half of a measuring unit

Example 3

• You use a beam balance to find the mass of a rock sample for a science lab. You read the scale as 3.8 g. What is your greatest possible error?

Example 3a

• You measure a picture for the yearbook and record its height as 9 cm. What is your greatest possible error?

Example 4

• You measure a room with dimensions of 13 ft and 7 ft. Use the greatest possible error to find the maximum and minimum possible areas.

Example 4a

• You measure a wall of your room as 8 ft high and 12 ft wide. Find the minimum and maximum possible areas of the wall.

Percent Error

• Percent error = greatest possible errormeasurement

Example 5

• Suppose you measure a CD and record its diameter as 12.1 cm. Find the percent error in your measurement.

Example 5a

• You measure the length of a table as 168 inches. Find the percent error in this measurement.

Example 5b

• You measure the length of a table as 168.0 inches. Find the percent error in this measurement.

Example 6

• A cassette case is 10.9 cm long, 6.8 cm wide, and 1.6 cm thick. Find the percent error in calculating its volume.

Example 6a

• Suppose you measured your math book and recorded the dimensions as 1 in x 9 in x 10 in. Find the percent error in calculating its volume.

Homework

• P. 171

• 2-38 even