Finding Perimeter and Area of Irregular Figures Notes-Practice

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May 12, 2013 ... 2 cm. Finding Perimeter and Area of Irregular Figures. Notes/Practice. Perimeter Notes. Sample 1. To find the perimeter of an irregular figure:.
Grade 5 Mathematics Unit: 09 Lesson: 03

Finding Perimeter and Area of Irregular Figures Notes/Practice Perimeter Notes Sample 1 To find the perimeter of an irregular figure: •

2.6 cm

Add all the side lengths.

2.5 cm

2.6 + 2.5 + 2 + 3.3 + 1.6 = 12

The perimeter is 12 cm.

1.6 cm

2 cm 3.3 cm

Sample 2 To find the length of an unknown side of an irregular figure when the perimeter is known: •

Find the length of side x if the perimeter of the figure equals 50 feet.

x

P = sum of the side lengths 50 = x + 16 + 6 + 4 + 19 50 = x + 45 50 – 45 = x x = 5; because 45 + 5 = 50

19 ft

16 ft

Side x is 5 feet long.

4 ft

©2012, TESCCC

05/12/13

6 ft

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Grade 5 Mathematics Unit: 09 Lesson: 03

Finding Perimeter of Irregular Figures Notes/Practice Perimeter and Area Notes Sample

15 in.

Find the perimeter and area of this polygon. 7 in. 5 in.

11 in.

4 in.

? •

First, find the unknown side length.



Look at the sides opposite the unknown side. Their measures are 15 in. and 5 in. The unknown side is 15 + 5 or 20 inches long.

15 in. 7 in. 5 in.

Find the perimeter using the sum of the side lengths.

11 in.

4 in.

P = 4 + 5 + 7 + 15 + 11 + 20 = 62 in.

5 in. + 15 in. = 20 in.



15 in.

The area of this figure can be found by calculating the area of the small rectangle and adding it to the large rectangle. A = (4 x 5) + (15 x 11) = 185 in

7 in.

2

5 in. 4 in.

15 x 11

11 in.

4x5

20 in.

©2012, TESCCC

05/12/13

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Grade 5 Mathematics Unit: 09 Lesson: 03

Finding Perimeter and Area of Irregular Figures Notes/Practice Practice: Use the figure itself and the space next to each figure to show your work and explain your reasoning. (1) Find the perimeter of this figure.

13 m 45 m 24 m

43 m (2)

What is the length of side x if the perimeter of this figure equals 941 mm?

218 mm

172 mm

183 mm

x 190 mm (3)

What is the perimeter of this polygon?

? 6 yd 11 yd

5 yd 5 yd 7 yd

©2012, TESCCC

05/12/13

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Grade 5 Mathematics Unit: 09 Lesson: 03

Finding Perimeter and Area of Irregular Figures Notes/Practice (4)

What is the area of this polygon?

? 6 yd 11 yd

5 yd 5 yd 7 yd

(5)

What is the perimeter of this polygon? 6m 4m 4m

?

5m 10 m

(6)

What is the area of this polygon? 6m 4m 4m

?

5m 10 m

©2012, TESCCC

05/12/13

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Grade 5 Mathematics Unit: 09 Lesson: 03

Finding Perimeter and Area of Irregular Figures Notes/Practice Use a ruler to determine the perimeter for each figure. (7)

1 inch = 27 feet

Perimeter in yards:

(8)

1 cm = 225 km

Perimeter in meters:

©2012, TESCCC

05/12/13

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