Learn on PengiIllustrative Mathematics, Grade 7Chapter 4: Proportional Relationships and Percentages

Lesson 3: Applying Percentages

In this Grade 7 lesson from Illustrative Mathematics Chapter 4, students apply percentages to calculate sales tax and tips in real-world contexts. They practice finding tax rates from given data, computing sales tax using fractional percentages such as 7.5%, and determining total cost as a percent increase of the original price. Students also work backwards from a known tax amount to find an original subtotal, building fluency with proportional reasoning.

Section 1

Sales Tax

Property

The sales tax is a percent of the purchase price.

Sales Tax=Tax Rate⋅Purchase Price\text{Sales Tax} = \text{Tax Rate} \cdot \text{Purchase Price}
Total Cost=Purchase Price+Sales Tax\text{Total Cost} = \text{Purchase Price} + \text{Sales Tax}

Section 2

Calculating Tips

Property

A tip (or gratuity) is calculated as a percentage of the subtotal, which is the cost of goods or services before sales tax is added.

Tip Amount=Subtotal×Tip Percentage \text{Tip Amount} = \text{Subtotal} \times \text{Tip Percentage}
Total Bill=Subtotal+Sales Tax+Tip Amount \text{Total Bill} = \text{Subtotal} + \text{Sales Tax} + \text{Tip Amount}

Lesson overview

Expand to review the lesson summary and core properties.

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Section 1

Sales Tax

Property

The sales tax is a percent of the purchase price.

Sales Tax=Tax Rate⋅Purchase Price\text{Sales Tax} = \text{Tax Rate} \cdot \text{Purchase Price}
Total Cost=Purchase Price+Sales Tax\text{Total Cost} = \text{Purchase Price} + \text{Sales Tax}

Section 2

Calculating Tips

Property

A tip (or gratuity) is calculated as a percentage of the subtotal, which is the cost of goods or services before sales tax is added.

Tip Amount=Subtotal×Tip Percentage \text{Tip Amount} = \text{Subtotal} \times \text{Tip Percentage}
Total Bill=Subtotal+Sales Tax+Tip Amount \text{Total Bill} = \text{Subtotal} + \text{Sales Tax} + \text{Tip Amount}