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# Perimeter and Area of Similar Figures PowerPoint PPT Presentation

7 th Grade Math Lesson Objective: Students will find the perimeter and area of similar figures. Perimeter and Area of Similar Figures. Concept – Perimeter. How to find Add each side length of an object Similar Figures Rule P (New) = P (Original) • SF Scale Factor New / Original.

Perimeter and Area of Similar Figures

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Lesson Objective:

Students will find the perimeter and area of similar figures.

## Perimeter and Area of Similar Figures

### Concept – Perimeter

• How to find

• Add each side length of an object

• Similar Figures Rule

• P(New)= P(Original)• SF

• Scale Factor

• New/Original

### Example 1

• Two rectangles are similar. One has a length of 6 inches and a perimeter of 24 inches. The other has a length of 7 inches. What is the perimeter of this rectangle?

SF = 7/6

P = 24 • 7/6

P = 28 in

### Example 2

L

P

18 m

24 m

Q

R

M

N

P = 64 m

LMN is similar to PQR

P = 64 • 3/4

SF = 18/24 or 3/4

P = 48 m

### Concept – Area

• How to find

• Rectangle = bh

• Triangle = ½bh

• Similar Figures Rule

• A(New)= A(Original)• SF2

• Scale Factor

• New/Original

### Example 3

• The Eddingtons have a 5-foot by 8-foot porch on the front of their house. They are building a similar porch on the back with double the dimensions. Find the area of the back porch.

A = 40 • 22

SF = 2

A = 40 • 4

A = 160 ft2

### Example 4

• Malia is painting a mural on her bedroom wall. The image she is reproducing is 1/20 of her wall and has an area of 36 square inches. Find the area of the mural.

A = 36 • 202

SF = 20

A = 36 • 400

A = 14,400 in2

### Example 5

• A company wants to reproduce the size of its logo by one fourth to use on business cards. If the area of the original logo is 4 square inches, what is the area of the logo that will be used on the business cards?

A = 4 • (¼)2

SF = ¼

A = 4 • 1/16

A = 0.25 in2