1. 2-8
Percents
Lesson Presentation
Lesson Quiz
Holt Algebra 1

2. Objective
Solve problems involving percents.

3.  Example 1A Find 30% of 80. Method 1 Use a proportion.
Use the percent proportion.
Let x represent the part.
100x = 2400
Find the cross products.
Since x is multiplied by 100, divide both sides by 100 to undo the multiplication.
x = 24
30% of 80 is 24.
Check 30% is the same as , and of 80 is 24. 

4. Example 1B
Find 4% of 36.
Method 2 Use an equation.
x = 4% of 36
Write an equation. Let x represent the part.
x = .04(36)
Write the percent as a decimal and multiply.
x =1.44
4% of 36 is 1.44.

5. 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.

6. 1D
230 is what percent of 200?
Method 2 Use a equation.
230 = x • 200
Write an equation. Let x represent the percent.
230 = 200x
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
Write the decimal as a percent. This answer is reasonable; 230 is more than 100% of 200.
230 is 115% of 200.

7. 1E
20 is 0.4% of what number?
Method 2 Use an equation.
Write an equation. Let x represent the whole.
20 = 0.4% of x
20 = • x
Write the percent as a decimal.
Since x is multiplied by 0.004, divide both sides by to undo the multiplication.
5000 = x
20 is 0.4% of 5000.

8. 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.

9. 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.
total pay = base salary + commission
Write the formula for total pay.
= base + % of total sales
Write the formula for commission.
= % of 940
Substitute values given in the problem.
= (0.12)(940)
Write the percent as a decimal. =
Multiply. =
Add.
The telemarketer’s total pay was $

10. Example 2C
Lunch at a restaurant is $ Estimate a 15% tip and determine the total bill.
Step 1 First round $27.88 to $30.
Step 2 Think: 15% = 10% + 5% % of $30 = $3.00
Move the decimal point one place left.
Step 3 Think 5% = 10% ÷ 2
= $3.00 ÷ 2 = $1.50
Step 4 15 = 10% + 5% = $ $1.50 = $4.50
The tip should be about $4.50. Total bill is $32.38

11. 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.
Move the decimal point two places left.
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.

12. Example 3A: Discounts
A student paid $31.20 for art supplies that normally cost $ Find the percent discount .
Think: is what percent of 52.00? Let x represent the percent.
$52.00 – $31.20 = $20.80
20.80 = x(52.00)
Since x is multiplied by 52.00, divide both sides by to undo the multiplication.
0.40 = x
40% = x
Write the answer as a percent.
The discount is 40%

13. 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%
The bicycle was 60% off of 100% .
0.40(220) = 88
Find 40% of 220. This is the discount from the original price.
220 – 88 = 142
By this method, the discount is $88. The sale price is $