7 th grade math lesson objective students will find the perimeter and area of similar figures
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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.

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7 th grade math lesson objective students will find the perimeter and area of similar figures

7th Grade Math

Lesson Objective:

Students will find the perimeter and area of similar figures.

Perimeter and Area of Similar Figures


Concept perimeter
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
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
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
Concept – Area

  • How to find

    • Rectangle = bh

    • Triangle = ½bh

  • Similar Figures Rule

    • A(New)= A(Original)• SF2

  • Scale Factor

    • New/Original


Example 3
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
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
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


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