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2-8
Percents
2-8 Percents
Lesson Presentation
Lesson Quiz
Holt Algebra 1
2-8
Percents
Objective
Solve problems involving percents.
Holt Algebra 1
2-8
Percents
Example 1A
Find 30% of 80.
Method 1 Use a proportion.
Use the percent proportion.
Let x represent the part.
100x = 2400
x = 24
30% of 80 is 24.
Find the cross products.
Since x is multiplied by 100, divide
both sides by 100 to undo the
multiplication.
Check 30% is the same as
Holt Algebra 1
, and
of 80 is 24.
2-8
Percents
Example 1B
Find 4% of 36.
Method 2 Use an equation.
x = 4% of 36
x = .04(36)
x =1.44
4% of 36 is 1.44.
Holt Algebra 1
Write an equation. Let x
represent the part.
Write the percent as a decimal
and multiply.
2-8
Percents
Example 1C
What percent of 45 is 35? Round your answer to
the nearest tenth.
Method 1 Use a proportion.
Use the percent proportion.
Let x represent the percent.
45x = 3500
Find the cross products.
Since x is multiplied by 45, divide
both sides by 45 to undo the
multiplication.
x ≈ 77.8
35 is about 77.8% of 45.
Holt Algebra 1
2-8
Percents
1D
230 is what percent of 200?
Method 2 Use a equation.
230 = x
200
230 = 200x
Write an equation. Let x represent
the percent.
Since x is multiplied by 200,
divide both sides by 200 to
undo the multiplication.
1.15 = x
The answer is a decimal.
•
115% = x
230 is 115% of 200.
Holt Algebra 1
Write the decimal as a percent.
This answer is reasonable; 230
is more than 100% of 200.
2-8
Percents
1E
20 is 0.4% of what number?
Method 2 Use an equation.
20 = 0.4% of x
20 = 0.004
•
x
5000 = x
20 is 0.4% of 5000.
Holt Algebra 1
Write an equation. Let x represent
the whole.
Write the percent as a decimal.
Since x is multiplied by 0.004,
divide both sides by 0.004 to
undo the multiplication.
2-8
Percents
Example 2A: Application
The serving size of a popular orange drink is
12 oz. The drink is advertised as containing
5% orange juice. How many ounces of orange
juice are in one serving size?
Use the percent proportion.
Let x represent the percent.
100x = 60
Since x is multiplied by 100, divide
both sides by 100 to undo the
multiplication.
x = 0.6
A 12 oz orange drink contains 0.6 oz of orange juice.
Holt Algebra 1
2-8
Percents
Example 2B
A telemarketer earns $350 per week plus
12% commission on sales. Find her total pay
for a week in which her sales were $940.
Write
the formula for total pay.
total pay = base salary
+ commission
the formula
= base + %Write
of total
sales for commission.
Substitute
values given in the problem.
= 350 + 12%
of 940
Write the percent as a decimal.
= 350 + (0.12)(940)
= 350 + 112.80
Multiply.
= 462.80 Add.
The telemarketer’s total pay was $462.80.
Holt Algebra 1
2-8
Percents
Example 2C
Lunch at a restaurant is $27.88. Estimate a
15% tip and determine the total bill.
Step 1 First round $27.88 to $30.
Step 2 Think: 15% = 10% + 5% Move the decimal
point one place left.
10% of $30 = $3.00
Step 3 Think 5% = 10% ÷ 2
= $3.00 ÷ 2 = $1.50
Step 4 15 = 10% + 5%
= $3.00 + $1.50 = $4.50
The tip should be about $4.50. Total bill is $32.38
Holt Algebra 1
2-8
Percents
Example 2D
The sales tax rate is 7.25%. Estimate the sales
tax on a book that costs $19.97.
Step 1 First round 7.25% to 7% and
$19.97 to $20.
Step 2 Think: 7% = 7(1%)
1% of $20 =$0.20
Step 3 7% = 7(1%)
= 7($0.20) = $1.40
The sales tax is about $1.40.
Holt Algebra 1
Move the decimal
point two places left.
2-8
Percents
Example 3A: 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.
2-8
Percents
Example 3B
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
220 – 88 = 142
The bicycle was 60% off of
100% .
Find 40% of 220. This is the
discount from the original
price.
By this method, the discount is $88. The sale price
is $142.00.
Holt Algebra 1