7 th Grade Math Lesson Objective: Students will find the 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 SF = 18 / 24 or 3 / 4 P = 64 3 / 4 P = 48 m L M N 24 m P Q R 18 m LMN is similar to PQR P = 64 m

Concept – Area How to find  Rectangle = bh  Triangle = ½bh Similar Figures Rule  A (New) = A (Original) SF 2 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. SF = 2 A = A = 40 4 A = 160 ft 2

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. SF = 20 A = A = A = 14,400 in 2

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? SF = ¼ A = 4 (¼) 2 A = 4 1 / 16 A = 0.25 in 2