Applications of Percent

Warm UpComplete the Table

Percent Fraction Decimal50%

¼ 0.04

35% 0.350.065

Vocabulary

• Sales tax, which is tax on the sale of an item or service, is a percent of the purchase price that is collected by the seller.

• When you deposit money in a savings account, your money usually earns interest. When you borrow money, you must pay back the original amount of the loan plus interest. Simple interest is a fixed percent of the principal. The principal is the original amount deposited or borrowed.

Marcus buys a varsity jacket from a clothing store in Anaheim. The price of the jacket is $80.00 and the sales tax is 8%. What is the total cost of the jacket?

Method 1 – Use a Bar Model

Method 2 Step 1: Write the percent as a decimal.

8% → 0.08

Step 2: Multiply the decimal times the cost of the jacket.

0.08 x $80.00 = $6.40

Step 3: Add the product from step 2 to the cost of the jacket.

Jacket Price + Sales Tax = Total Cost$80.00 + $6.40 = $86.40

Sharon wants to buy a shirt that costs $20.00. The sales tax is 5%. How much is the sales tax? What is her total cost for the shirt?

Terry deposits $200.00 into a bank account that earns 3% interest per year. What is the total amount in the account after 2 years?

Is there another way?

Can we find an expression that works for simple interest?

Ariane borrows $400.00 on a 4 year loan. She is charged 5% simple interest per year. How much interest is she charged for 4 years? What is the total amount she has to pay back?

The Sanchez family goes out for dinner, and the price of the meal is $60.00. The sales tax on the meal is 7%, and they also want to leave a 15% tip. What is the total cost of the meal?

Formulate a Plan

Calculate the sales tax separately, then calculate the tip, and then add the products to the bill for the meal to find the total.

Justify and Evaluate

Estimate the sales tax and tip.

Sales tax is about 10% plus 15% for tip gives 25%.

Find 25% of the bill: 0.25 x $60.00 = $15.00.

Add this to the bill: $60.00 + $15.00 = $75.00.

The total cost should be about $75.00.

Kedar earns a monthly salary of $2,200.00 plus 3.75% commission on the amount of his sales at a men’s clothing store. One month he sold $4,500.00 in clothing. What was his commission that month? How much did he earn in all?