1. Applications of Percents
2-9
Applications of Percents
Holt Algebra 1
Warm Up
Lesson Presentation
Lesson Quiz

2. Lesson Quiz: Part 1
Find each value. Round to the nearest tenth if necessary.
Find 20% of 80.
2. What percent of 160 is 20?
3. 35% of what number is 40?
is what percent of 80? 16
12.5%
114.3
150%

3. Warm Up 1. Write 0.03 as a percent. 2. Write as a decimal.
Find each value. Round to the nearest tenth
if necessary.
3. Find 10% of 53.
Solve for x.
5. 40 = (x) (20) 3%
0.045
4. Find of 50.
5.3
1.3
= (36) (x) 4 38

4. Objectives Use common applications of percents.
Estimate with percents.

5. Vocabulary
commission
interest
sales tax
principal
tip

6. Percent Proportion
3 out of 5

7. Percent Proportion
What is 25% of 20? 5

8. Percent Proportion
5 is what percent of 20?
.25 or 25%

9. 5. Find 320% of 8.
25.6
6. 65 is 0.5% of what number?
13,000

10. A commission is money paid to a person or a company for making a sale
A commission is money paid to a person or a company for making a sale. Usually the commission is a percent of the sale amount.

11. Caution!
You must convert a percent to a decimal or a fraction before doing any calculations with it.

12. Example 1: Business Application
Mr. Cortez earns a base salary of $26,000 plus a sales commission of 5%. His total sales for one year were $300,000. Find his total pay for the year.
total pay = base salary + commission
Write the formula for total pay.
= base + % of total sales
Write the formula for commission.
= 26, % of 300,000
Substitute values given in the problem.
= 26,000 + (0.05)(300,000)
Write the percent as a decimal.
= 26, ,000
Multiply.
= 41,000
Add.
Mr. Cortez’s total pay was $41,000.

13. I = P r t Simple Interest Paid Annually
Interest is the amount of money charged for borrowing money, or the amount of money earned when saving or investing money. Principal is the amount borrowed or invested. Simple interest is interest paid only on the principal.
Simple Interest Paid Annually I = P r t
Simple interest
Time in years
Principal
Interest rate per
year as a decimal

14. Example 2A: Financial Application
Find the simple interest paid for 3 years on a $2500 loan at 11.5% per year.
I = Prt
Write the formula for simple interest.
I = (2500)(0.115)(3)
Substitute known values. Write the interest rate as a decimal.
I =
Multiply.
The amount of interest is $

15. Example 2B: Financial Application
After 6 months, the simple interest earned on an investment of $5000 was $45. Find the interest rate.
Write the formula for simple interest.
I = Prt
Substitute the given values.
Multiply Since r is multiplied by 2500, divide both sides by 2500 to undo the multiplication.
45 = 2500r
0.018 = r
The interest rate is 1.8%.

16. Helpful Hint
When you are using the formula I= Prt to find simple interest paid annually, t represents time in years. One month is year.

17. A tip is an amount of money added to a bill for service
A tip is an amount of money added to a bill for service. it is usually a percent of the bill before sales tax is added. Sales tax is a percent of an item’s cost.

18. Sales tax and tips are sometimes estimated instead of calculated exactly. When estimating percents, use percents that you can calculate mentally.
Find 10% of a number by moving the decimal point one place to the left.
Find 1% of a number by moving the decimal point two places to the left.
Find 5% of a number by finding of 10% of the number.

19. Example 3A: Estimating with Percents
Lunch at a restaurant is $ Estimate a 15% tip.
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.

20. Example 3B: Estimating with Percents
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.

21. Helpful Hint
A 6.25% sales tax rate means that for every $100 you spend, you would pay $6.25 in sales tax.

22. Lesson Quiz: Part 1
1. A computer salesperson earns a base salary of $32,000 per year plus a commission of 6% on total sales. Total sales for one year were $350,000. Find the salesperson’s total pay for the year.
$53,000
2. Find the simple interest paid for 9 months on a a $500 loan at 8% per year.
$30
3. After 2 years the simple interest earned on an investment of 4000 was $216. Find the interest rate.
2.7%

23. Lesson Quiz: Part 2
4. A family’s dinner check was $ Estimate a 15% tip.
About $6.00
5.The sales tax rate is 7.1%. Estimate the sales tax on a television set that costs $399.
About $28