Percent of Change Percent of Change

Tuesday, October 19, 2010Tuesday, October 19, 2010

Lesson ObjectivesLesson Objectives

Find percent of change (percent of Find percent of change (percent of increase or percent of decrease)increase or percent of decrease)

Real-Life ConnectionReal-Life Connection

What things in everyday life are described What things in everyday life are described as % increases or % decreases? as % increases or % decreases?

What things in everyday life are described as What things in everyday life are described as percent increases or decreases?percent increases or decreases?

Fuel pricesFuel prices (example: The cost of gas might (example: The cost of gas might increase by 10% over a major holiday increase by 10% over a major holiday weekend)weekend)

Other product pricesOther product prices (example: You might go (example: You might go shopping and find a sweater that’s 20% off)shopping and find a sweater that’s 20% off)

The stock market The stock market (example: You may read in (example: You may read in the newspaper that a corporation’s shares the newspaper that a corporation’s shares have risen 1.8%)have risen 1.8%)

Any increase or decrease can be Any increase or decrease can be represented as a percent! represented as a percent!

VocabularyVocabulary

A percent of change is a ratioA percent of change is a ratio It compares the change in quantity to the It compares the change in quantity to the

original amount original amount

change in quantity change in quantity __________________ __________________

original amount original amount

This is your formula for finding This is your formula for finding percent of change!percent of change!

change in quantity change in quantity _______________ _______________

original amount original amount

VocabularyVocabulary

If the original amount goes up, or If the original amount goes up, or increases, then it is a increases, then it is a percent of percent of increaseincrease

If the original amount goes down, or If the original amount goes down, or decreases, then it is a decreases, then it is a percent of percent of decreasedecrease

Example 1Example 1

Let’s say you are shopping for a jacketLet’s say you are shopping for a jacket The original cost of the jacket is $50The original cost of the jacket is $50 The jacket is on sale for $35The jacket is on sale for $35

Is this situation an Is this situation an increaseincrease or or decreasedecrease? ?

Example 1Example 1

Use the percent of change formula to find Use the percent of change formula to find the percent of the percent of decreasedecrease in the costin the cost

Example 1 – step one: apply the Example 1 – step one: apply the formulaformula

change in cost = $50 – 35 = $ 15change in cost = $50 – 35 = $ 15

___________ _______ _______________ _______ ____

original cost $50 $50original cost $50 $50

Example 1 – step two: convert Example 1 – step two: convert the ratio to a percentthe ratio to a percent

$15 15 30$15 15 30

___ or ___ = ___ = 30%___ or ___ = ___ = 30%

$50 50 100 $50 50 100

Example 1 – solutionExample 1 – solution

The price of the jacket was decreased The price of the jacket was decreased by 30%by 30%

In other words, the jacket was on sale In other words, the jacket was on sale for 30% off for 30% off

Example 2 Example 2

Rita weighed 120 pounds on Thanksgiving. Rita weighed 120 pounds on Thanksgiving. On New Year’s Day, she weighed 130 On New Year’s Day, she weighed 130 pounds. Find the percent of change in pounds. Find the percent of change in Rita’s weight from Thanksgiving to New Rita’s weight from Thanksgiving to New Year’s Day and state whether it is an Year’s Day and state whether it is an increase or a decrease.increase or a decrease.

Example 2 – step one: apply the Example 2 – step one: apply the formulaformula

change in weight = 130 – 120 = 10 change in weight = 130 – 120 = 10

_____________ _______ _________________ _______ ____

original weightoriginal weight 120 120 120120

Example 2 – step one: convert the Example 2 – step one: convert the ratio to a percentratio to a percent

10 10

___ = 8.333333% or 8.3%___ = 8.333333% or 8.3%

120 120

Example 2 – solutionExample 2 – solution

From Thanksgiving to New Year’s Day, Rita’s From Thanksgiving to New Year’s Day, Rita’s weight increased by approximately 8.3%weight increased by approximately 8.3%

Let’s Review! Let’s Review!

1. What is the formula for finding 1. What is the formula for finding percent of change? percent of change?

Let’s Review! Let’s Review!

1. What is the formula for finding 1. What is the formula for finding percent of change? percent of change? change in quantity change in quantity

_______________ _______________

original amount original amount

Let’s Review! Let’s Review!

2. What do you do with the ratio you 2. What do you do with the ratio you get after you have applied the get after you have applied the formula?formula?

Let’s Review! Let’s Review!

2. What do you do with the ratio you 2. What do you do with the ratio you get after you have applied the get after you have applied the formula? formula? Convert it to a percent! Convert it to a percent!

Let’s Review! Let’s Review!

3. How do you know if it’s a percent 3. How do you know if it’s a percent of increase or a percent of decrease?of increase or a percent of decrease?

Let’s Review! Let’s Review!

3. How do you know if it’s a percent 3. How do you know if it’s a percent of increase or a percent of decrease?of increase or a percent of decrease?Did the original amount go up or Did the original amount go up or down?down?