Download 2.10

2-10 Percent Increase and Decrease
Warm Up
1. Find 30% of 40.
12
2. Find 28% of 60.
16.8
Solve for x.
3. 22 = x(50)
0.44
4. 17.2 = x(86) 38
5. 20 is what percent of 80?
25%
6. 36 is what percent of 30? 120%
Holt Algebra 1
2-10 Percent Increase and Decrease
Objective
Find percent increase and decrease.
Holt Algebra 1
2-10 Percent Increase and Decrease
A percent change is an increase or decrease
given as a percent of the original amount.
Percent increase describes an amount that
has grown and percent decrease describes
an amount that has be reduced.
Holt Algebra 1
2-10 Percent Increase and Decrease
Example 1A: Finding Percent Increase and Decrease
Find each percent change. Tell whether it is a
percent increase or decrease.
From 8 to 10
Simplify
Simplifythe
thenumerator.
fraction.
= 0.25
Write the answer as a percent.
= 25%
8 to 10 is an increase, so a change from 8 to 10
is a 25% increase.
Holt Algebra 1
2-10 Percent Increase and Decrease
Example 1B: Finding Percent Increase and Decrease
Find the percent change. Tell whether it is a
percent increase or decrease.
From 75 to 30
Simplify
Simplifythe
thefraction.
numerator.
= 0.6
Write the answer as a percent.
= 60%
75 to 30 is a decrease, so a change from 75 to
30 is a 60% decrease.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 1a
Find each percent change. Tell whether it is a
percent increase or decrease.
From 200 to 110
Simplify
numerator.
Simplify
thethe
fraction.
= 0.6
Write the answer as a percent.
= 60%
200 to 110 is an decrease, so a change from 200
to 110 is a 60% decrease.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 1b
Find each percent change. Tell whether it is a
percent increase or decrease.
From 25 to 30
Simplifythe
thefraction.
numerator.
Simplify
= 0.20
Write the answer as a percent.
= 20%
25 to 30 is an increase, so a change from 25 to
30 is a 20% increase.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 1c
Find each percent change. Tell whether it is a
percent increase or decrease.
From 80 to 115
Simplifythe
thefraction.
numerator.
Simplify
= 0.4375
= 43.75% Write the answer as a percent.
80 to 115 is an increase, so a change from 80 to
115 is a 43.75% increase.
Holt Algebra 1
2-10 Percent Increase and Decrease
Example 2: Finding Percent Increase and Decrease
A. Find the result when 12 is increased by 50%.
Find 50% of 12. This is the amount of
increase.
It is a percent increase, so add 6 to
12 + 6 =18
the original amount.
12 increased by 50% is 18.
B. Find the result when 55 is decreased by 60%.
Find 60% of 55. This is the amount of
0.60(55) = 33
decrease.
It is a percent decrease so subtract
55 – 33 = 22
33 from the the original amount.
0.50(12) = 6
55 decreased by 60% is 22.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 2
A. Find the result when 72 is increased by 25%.
Find 25% of 72. This is the amount of
increase.
It is a percent increase, so add 18 to
72 + 18 =90
the original amount.
72 increased by 25% is 90.
B. Find the result when 10 is decreased by 40%.
Find 40% of 10. This is the amount of
0.40(10) = 4
decrease.
It is a percent decrease so subtract 4
10 – 4 = 6
from the the original amount.
0.25(72) = 18
10 decreased by 40% is 6.
Holt Algebra 1
2-10 Percent Increase and Decrease
Common application of percent change are discounts
and markups.
A discount is an
discount = % of original price
amount by which
an original price is final price = original price – discount
reduced.
A markup is an
markup = % of wholesale cost
amount by which
a wholesale price final price = wholesale cost + markup
is increased.
Holt Algebra 1
2-10 Percent Increase and Decrease
Example 3: Discounts
The entrance fee at an amusement park is
$35. People over the age of 65 receive a
20% discount. What is the amount of the
discount? How much do people over 65 pay?
Method 1 A discount is a percent decrease. So
find $35 decreased by 20%.
0.20(35) = 7
35 – 7 = 28
Holt Algebra 1
Find 20% of 35. This is the amount
of the discount.
Subtract 7 from 35. This is the
entrance fee for people over the
age of 65.
2-10 Percent Increase and Decrease
Example 3A: Discounts
Method 2 Subtract the percent discount from
100%.
100% – 20% = 80%
0.80(35) = 28
35 – 28 = 7
People over the age of 65 pay
80% of the regular price, $35.
Find 80% of 35. This is the
entrance fee for people over
the age of 65.
Subtract 28 from 35. This is the
amount of the discount.
By either method, the discount is $7. People over
the age of 65 pay $28.00.
Holt Algebra 1
2-10 Percent Increase and Decrease
Example 3B: Discounts
A student paid $31.20 for art supplies that
normally cost $52.00. Find the percent
discount .
Think: 20.80 is what
$52.00 – $31.20 = $20.80
percent of 52.00? Let x
20.80 = x(52.00)
represent the percent.
Since x is multiplied by
52.00, divide both sides
by 52.00 to undo the
0.40 = x
multiplication.
40% = x
The discount is 40%
Holt Algebra 1
Write the answer as a
percent.
2-10 Percent Increase and Decrease
Check It Out! Example 3a
A $220 bicycle was on sale for 60% off.
Find the sale price.
Method 2 Subtract the percent discount from
100%.
100% – 60% = 40%
0.40(220) = 88
The bicycle was 60% off of
100% .
Find 40% of 220.
By this method, the sale price is $88.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 3b
Ray paid $12 for a $15 T-shirt. What was
the percent discount ?
$15 – $12 = $3
3 = x(15)
0.20 = x
20% = x
The discount is 20%.
Holt Algebra 1
Think: 3 is what percent of
15? Let x represent the
percent.
Since x is multiplied by 15,
divide both sides by 15 to
undo the multiplication.
Write the answer as a percent.
2-10 Percent Increase and Decrease
Example 4: Markups
The wholesale cost of a DVD is $7. The
markup is 85%. What is the amount of the
markup? What is the selling price?
Method 2
1
A
markup
is a
percenttoincrease.
Add
percent
markup
100% So find $7
increased by 85%.
Find 85% of 7. This is the amount
The
selling price is 185% of the
100%
0.85(7)+=85%
5.95= 185%
of the markup.
wholesale price, 7.
Find
185%
of 7.
is the selling
1.85(7)
7 + 5.95==12.95
12.95
Add to
7. This
is This
the selling
price.
price.
12.95  7 = 5.95
Subtract from 12.95. This is the
amount of the markup.
By either method, the amount of the markup
is $5.95. The selling price is $12.95.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 4
A video game has a 70% markup. The wholesale
cost is $9. What is the selling price?
Method 1
A markup is a percent increase. So find $9 increased
by 70%.
0.70(9) = 6.30
Find 70% of 9. This is the amount
of the markup.
9 + 6.30 = 15.30
Add to 9. This is the selling price.
The amount of the markup is $6.30. The selling price
is $15.30.
Holt Algebra 1
2-10 Percent Increase and Decrease
Check It Out! Example 4
What is the percent markup on a car selling for
$21,850 that had a wholesale cost of $9500?
21,850 – 9,500 = 12,350
12,350 = x(9,500)
1.30 = x
130% = x
Find the amount of the markup.
Think: 12,350 is what percent of
9,500? Let x represent the
percent.
Since x is multiplied by 9,500
divide both sides by 9,500
to undo the multiplication.
Write the answer as a percent.
The markup was 130 percent.
Holt Algebra 1
2-10 Percent Increase and Decrease
Lesson Quiz: Part 1
Find each percent change. Tell whether it is a
percent increase or decrease.
1. from 20 to 28.
40% increase
2. from 80 to 62.
22.5% decrease
3. from 500 to 100.
80% decrease
4. find the result when 120 is increased by 40%. 168
5. find the result when 70 is decreased by 20%.
Holt Algebra 1
56
2-10 Percent Increase and Decrease
Lesson Quiz: Part 2
Find each percent change. Tell whether it is a
percent increase or decrease.
6. A movie ticket costs $9. On Mondays, tickets are
20% off. What is the amount of discount? How
much would a ticket cost on a Monday?
$1.80; $7.20
7. A bike helmet cost $24. The wholesale cost was
$15. What was the percent of markup?
60%
Holt Algebra 1
2-10 Percent Increase and Decrease
Home work pg. 141
16-34 evens
46,48,58,60,62
Holt Algebra 1