Pre-Algebra 8-4 Percent Increase and Decrease Our Learning Goal Students will be able to determine and construct fractions, decimals, and percents by understanding.

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Pre-Algebra

8-4 Percent Increase and Decrease

Our Learning GoalStudents will be able to determine and construct fractions, decimals, and percents by understanding their relationships, solving for the unknown, solving increase and decrease, solving sales tax/total cost contextual problems and compute simple interest.

Pre-Algebra


Pre-Algebra HOMEWORKPage 412-413

#17-25 &

Spiral Review

ANSWERS

Pre-Algebra


Pre-Algebra Homework

Page 419

#30-36 & Spiral Review (#37-40)

Our Learning Goal Assignments

• Learn to relate decimals, fractions, & percents (8-1)

• Learn to find percents (8-2)

• Learn to find a number when the percent is known (8-3)

• Learn to find percent increase and decrease (8-4)

• Learn to estimate with percents (8-5)

• Learn to find commission, sales tax, and withholding tax (8-6)

• Learn to compute simple interest (8-7)

Pre-Algebra

8-4 Percent Increase and DecreaseLearning Goal Scale

Students are able to determine & construct fractions, decimals, & percents:

4 3 2 1 0

• Clear understanding their relationships

• Able to solve for the unknown

• Understands how to solve for increase & decrease

• Calculating solving sales tax/total cost contextual problems

• Computing simple interest

• Understands their relationships

• Some solving for the unknown

• Difficulty solving for increase & decrease

• Understands their relationships

• Difficulty solving for the unknown

• Some understanding their relationships

• Even with help, no understanding or skill demonstrated

Pre-Algebra


Student Learning Goal Chart

Pre-Algebra

8-4 Percent Increase and Decrease8-4 Percent Increase and Decrease

Pre-Algebra

Warm UpWarm Up

Problem of the DayProblem of the Day

Lesson PresentationLesson Presentation

Pre-Algebra


Warm Up

1. 14,000 is 2 % of what number?

2. 39 is 13% of what number?

3. 37 % of what number is 12?

4. 150% of what number is 189?

560,000

300

32

Pre-Algebra


12

126

12

Pre-Algebra


Problem of the Day

In a school survey, 45% of the students said orange juice was their favorite juice, 25% preferred apple, and 10% preferred grapefruit. The remaining 32 students preferred grape juice. How many students participated in the survey?

160 students

Pre-Algebra


Today’s Learning Goal Assignment

Learn to find percent increase and decrease.

Pre-Algebra


Vocabulary

percent changepercent increasepercent decrease

Pre-Algebra


Percents can be used to describe a change. Percent change is the ratio of the amount of change to the original amount.

Percent increase describes how much the original amount increases.

Percent decrease describes how much the original amount decreases.

amount of changeoriginal amountpercent change =

Pre-Algebra


Find the percent increase or decrease from 16 to 12.

Additional Example 1: Percent Increase and Decrease

This is percent decrease.

16 – 12 = 4 First find the amount of change.

Think: What percent is 4 of 16?

amount of decreaseoriginal amount

416

Set up the ratio.

Pre-Algebra


Additional Example 1 Continued

= 25% Write as a percent.

= 0.25 Find the decimal form.416

From 16 to 12 is a 25% decrease.

Pre-Algebra


Find the percent increase or decrease from 15 to 20.

Try This: Example 1

This is percent increase.



amount of increaseoriginal amount

520

Set up the ratio.

Pre-Algebra


Try This: Example 1 Continued


= 0.25 Find the decimal form.520

From 15 to 20 is a 25% increase.

Pre-Algebra


A. When Jim was exercising, his heart rate went from 70 beats per minute to 98 beats per minute. What was the percent increase?

Additional Example 2: Life Science Application


28 70

Set up the ratio.



Pre-Algebra


Additional Example 2 Continued


= 0.4 Find the decimal form. 70

28

Jim’s heart rate increased by 40% when he exercised.

Pre-Algebra


B. In 1999, a certain stock was worth $1.25 a share. In 2002, the same stock was worth $0.85 a share. What was the percent decrease?

Additional Example 2B: Application

1.25 – 0.85 = 0.40 First find the amount of change.

Think: What percent is 0.40 of 1.25?

amount of decreaseoriginal amount 1.25

0.40Set up the ratio.

Pre-Algebra


Additional Example 2B Continued


= 0.32 Find the decimal form. 1.25

0.40

The value of the stock decreased by 32%.

Pre-Algebra


A. When Jeff was watching TV, the number of times his eyelids blinked went from 50 blinks per minute to 75 blinks per minute. What was the percent increase?

Try This: Example 2A


25 50

Set up the ratio.



Pre-Algebra



= 0.5 Find the decimal form. 50

25

The blinking of Jeff’s eyelids increased by 50% when he watched TV.

Try This: Example 2A Continued

Pre-Algebra


B. In 2000, a certain stock was worth $9.00 a share. In 2003, the same stock was worth $3.80 a share. What was the percent decrease?

Try This: Example 2B

9.00 – 3.80 = 5.20 First find the amount of change.

Think: What percent is 5.20 of 9.00?

amount of decreaseoriginal amount 9.00

5.20Set up the ratio.

Pre-Algebra


The value of the stock decreased by about 57.8%.

9.005.20 = 0.57 Find the decimal form.

= 57.7% Write as a percent.

Try This: Example 2B Continued

Pre-Algebra


A. Sarah bought a DVD player originally priced at $450 that was on sale for 20% off. What was the sale price?

Additional Example 3A: Percent Increase and Decrease

$450 20% First find 20% of $450.

$450 0.20 = $90 20% = 0.20

The amount of decrease is $90.

Think: The reduced price is $90 less than $450.

$450 – $90 = $360 Subtract the amount of decrease.The sale price of the DVD player was $360.

Pre-Algebra


A. Lily bought a dog house originally priced at $750 that was on sale for 10% off. What was the sale price?

Try This: Example 3A

$750 10% First find 10% of $750.

$750 0.10 = $75 10% = 0.10

The amount of decrease is $75.

Think: The reduced price is $75 less than $750.

$750 – $75 = $675 Subtract the amount of decrease.

The sale price of the dog house was $675.

Pre-Algebra


B. Mr. Olsen has a computer business in which he sells everything at 40% above the wholesale price. If he purchased a printer for $85 wholesale, what will be the retail price?

Additional Example 3B: Percent Increase and Decrease

$85 40% First find 40% of $85.

$85 0.40 = $34 40% = 0.40

The amount of increase is $34.

Think: The retail price is $34 more than $85.

$85 + $34 = $119 Add the amount of increase.

The retail price of this printer will be $119.

Pre-Algebra


B. Barb has a grocery store in which she sells everything at 50% above the wholesale price. If she purchased a prime rib for $30 wholesale, what will be the retail price?

$30 50% First find 50% of $30.

$30 0.50 = $15 50% = 0.50

The amount of increase is $15.

Think: The retail price is $15 more than $30.

$30 + $15 = $45 Add the amount of increase.

The retail price of the prime rib will be $45.

Try This: Example 3B

Pre-Algebra


Textbook ClassworkDue at the end of the period!

You may work with ONE other person!

Page 414

#1-17

Pre-Algebra


Lesson QuizFind each percent increase or decrease to the nearest percent.

1. from 12 to 15

2. from 1625 to 1400

3. from 37 to 125

4. from 1.25 to 0.85

5. A computer game originally sold for $40 but is

now on sale for 30% off. What is the sale price of

the computer game?

14% decrease

25% increase

238% increase

32% decrease

$28

Pre-Algebra 8-4 Percent Increase and Decrease Our Learning Goal Students will be able to determine and construct fractions, decimals, and percents by understanding.

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