Answers
7. about 53.38 m
8. about 18.84 ft
9. about 88 in.
8.2 Warm Up
10. about 56.54 mm
11. about 20.56 in.
12. about 25.7 yd
13. a. 8 mm; 24 mm
b. 3 times greater
14. $131.56
15. about 5.14 ft
3. 52 in.
4. 25 m
5. about 56.52 in. 6. about 62.8 ft
Sample answer: yes; It is made up of a rectangle and two
semicircles. Some examples: windows (rectangle and
semicircle), some company and organization logos, a
first place ribbon (circle and rectangles), some flowers
2. about 37.68 ft
3. about 264 in.
4. about 72 yd
5. about 31.05 ft
6. about 28.27 cm
8.2 Warm Up
For use before Lesson 8.2
1. 24 units
2. 24 units
3.5 ft
3. about 15 units
4. about 13.71 units
84 in.
5. about 20.5 units
6. about 22.28 units
Circle
A
B
C
D
Radius
2.5 ft
1 ft
32 ft
Diameter
60 in.
24 in.
768 in.
8.2 Practice A
8. about 9.42 in.
9. yes; The diameter of each of the small circles in
diagram B is 2 feet. Because there are 5 circles
along each side of the square, the length of each
side is 5 • 2 = 10 feet.
10. about 9.6 times
1. about 24 in.
2. about 28 in.
3. about 21.42 in.
4. 34 yd
5. 24 in.
6. 60 mm
7. 31 m
8. 24 ft
9. 64 cm
10. about 23.42 ft
11. $3685.90
8.2 Practice B
8.1 Enrichment and Extension
2. 43.96 ft, 87.92 ft
3. 47.1 cm, 94.2 cm
4. The circumference is multiplied by 2.
5. The circumference is multiplied by n.
6. 12.85 mm, 6.425 mm
2. 17 ft
For use before Lesson 8.2
1. about 81.64 m
1. 25.12 in., 50.24 in.
1. 16 cm
8.2 Start Thinking!
8.1 Practice B
7.
For use before Activity 8.2
7. 5.14 in., 2.57 in.
1. about 22 in.
2. 28 in.
3. about 22 in.
4. 27 m
5. about 140.76 cm
6. 28 in.
7. The perimeter calculation included the
circumference of the circle instead of the
perimeter of the semicircle.
Perimeter ≈ 2 + 7 + 2 + 10.99
8. 51.4 m, 25.7 m
9. The perimeter is multiplied by
= 21.99 ft
1
.
2
10. The perimeter is multiplied by n.
8. about $211.31
9. Sample answer:
10 ft
3 ft
8.1 Puzzle Time
HE HAD TOO MUCH TIME ON HIS HANDS
3 ft
8.2 Start Thinking!
18 ft
4 ft
For use before Activity 8.2
Sample answer: To find the perimeter of an irregular
shape, you can add all of the different straight sections
(or circular sections). To find a distance on a map,
assuming that the route traveled is not along a straight
line, you must add all of the straight sections to
estimate the total distance.
Copyright © Big Ideas Learning, LLC
All rights reserved.
9 ft
3 ft
yes; For example, if the 11 ft by 3 ft rectangle on
the bottom of the F is shortened to be a 6 ft by 3 ft
rectangle, the perimeter decreases by 10 ft.
Big Ideas Math Red
Answers
A41
Answers
8.2 Enrichment and Extension
1. about 25.12 in.
2. about 18.84 m
3. about 34.26 ft
4. about 30.26 yd
5. about 55.4 cm
6. about 50.24 mm
5. about 100.48 m 2
6. about 693 ft 2
7. about 2464 ft 2
8. about 28.26 ft 2
circle whose radius is twice as large; The area
formula for the smaller circle can be rewritten as
LIBRARY
2
8.3 Start Thinking!
1
r
A = π   = π r 2 ; this is one fourth of the
4
 2
area of the larger circle.
For use before Activity 8.3
Sample answer: 1. You can divide it into several
triangles each with a vertex at the center of the circle.
2. You can put it on grid paper and estimate the
number of squares that are covered. 3. You can divide
it into tall, narrow rectangles.
8.3 Warm Up
For use before Activity 8.3
4. 50 cm
2
2
c. The circle’s area is one fourth of the area of the
8.2 Puzzle Time
1. 63 in.2
r
 2
b. A = π  
9. a. A = π r 2
10. The radius is 2 units; Set the circumference
equal to the area to get 2π r = π r 2 .
So π • r • 2 = π • r • r ; the value
of r must be 2.
8.3 Enrichment and Extension
2. 14 m2
3. 66 yd 2
5. 22.4 m
2
6. 1 mm
1. 1.5625
2. 2.25
3. 16%
2
4.
1
9
5. a. 3.5%
8.3 Start Thinking!
b.
For use before Lesson 8.3
22
if the radius
7
is a multiple of 7. It is easier to use 3.14 in all other
instances. Check students’ word problems.
Sample answer: It is easier to use
8.3 Warm Up
For use before Lesson 8.3
1. about 50.24 in.2
13,816 mi 2
2. about 154 ft 2
c.
3. about 3.14 cm2
8.3 Practice A
1. about 78.5 m 2
2. about 7850 mm 2
3. about 1256 in.2
4. about 38.5 ft 2
5. about 1386 mm 2
6. about 3850 cm 2
7. about 50.24 ft 2
8. about 15,400 cm 2
2
9. about 113.04 in.
11.
99
in.2
224
2
10. about 28.26 in.
12. about 153.86 in.2
8.3 Practice B
1. about 962.5 in.2
2. about 19.625 m 2
3. about 7234.56 mm2
4. about 157 in.2
A42 Big Ideas Math Red
Answers
56,834 mi 2
8.3 Puzzle Time
HAMWORK
8.4 Start Thinking!
For use before Activity 8.4
Answers will vary. Sample answer: If you are planning
on painting a room, you will need to calculate the area
of each section of wall to figure out how much paint to
buy. The windows and doorways make some walls
composite figures.
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All rights reserved.