reteach area circle

Name Date Class
LESSON
10-5
Reteach
Area of Circles
To estimate the area A of a circle, use the formula A r 2 and 3 for .
A r 2
3 2 2
3 4
12 square units.
The area is about 12 square units.
Estimate the area of each circle. Use 3 for .
1.
3.
A are units
A 75 are units
1
5
Copyright © by Holt, Rinehart and Winston. 39 Holt Mathematics
All rights reserved.
2.
4.
r 2
A 48are units
A 27 suare units
4
3

Name Date Class
LESSON
10-5
Reteach
Area of Circles (continued)
To find the area A of a circle, use the formula A r 2 and 22
for .
7
A r 2
22
• 4
7
2
22
• 16
7
35
r 4
2
7
50.29 square units
The area is about 50.29 square units.
Find the area of each circle. Use 22
for . Round each answer
7
to the nearest hundredth.
5. 6.
A 28.29 sare units
7. 8.
A 12.57 suare units
2
3
A 3.14are units
A 78.57 suare units
Copyright © by Holt, Rinehart and Winston. 40 Holt Mathematics
All rights reserved.
1
5

LESSON
10-5
Reteach
Area of Circles
To estimate the area A of a circle, use the formula A r 2 and 3 for .
A r 2
3 2 2
3 4
12 square units.
The area is about 12 square units.
Estimate the area of each circle. Use 3 for .
1.
3.
1
A 3 square units
A 75 square units
5
Copyright © by Holt, Rinehart and Winston. 39 Holt Mathematics
All rights reserved.
LESSON
10-5
Challenge
Pies Are Squared
2.
4.
r 2
A 48 square units
A 27 square units
Have you ever heard the saying, “You can’t fit a square peg in a
round hole”? Well, sometimes you can fit a round pie in a square
dish—if you squeeze really hard and don’t mind messy areas.
Find the area of each pie and pie dish. Use 3.14 for , and
round your measurements to the nearest hundredth. Then
imagine you could squish the pies. Which square pan would
each round pie best fit in? Draw a line from the pie to the
appropriate pie dish.
1. A.
d 10 in.
Area 78.5 in Area
2
2. B.
r 6 in.
Area 113.04 in Area
2
3. C.
d 9 in.
Area 63.59 in Area
2
4. D.
r 7 in.
s 10.64 in.
s 12.41 in.
s 8.86 in.
s 7.98 in.
78.5 in 2
Area Area 63.68 in 2
153.86 in 2
Copyright © by Holt, Rinehart and Winston. 41 Holt Mathematics
All rights reserved.
4
3
113.21 in 2
154.01 in 2
Reteach
Area of Circles (continued)
To find the area A of a circle, use the formula A r 2 and 22
for .
7
A r 2
22
• 4
7
2
22
• 16
7
35
r 4
2
7
50.29 square units
The area is about 50.29 square units.
Find the area of each circle. Use 22
for . Round each answer
7
to the nearest hundredth.
5. 6.
A 28.29 square units
7. 8.
A 12.57 square units
A 78.57 square units
Copyright © by Holt, Rinehart and Winston. 40 Holt Mathematics
All rights reserved.
Copyright © by Holt, Rinehart and Winston. 86 Holt Mathematics
All rights reserved.
LESSON
10-5
LESSON
10-5
Problem Solving
Area of Circles
2
3
Use the table to answer each question. Use 3.14 for pi.
1. Which ring is the largest? What area does it enclose?
Ring 1; 5,024 cm 2
2. What is the area of the center circle, or the inner
10 scoring ring, on the target?
12.56 cm 2
3. What area does Ring 5 enclose?
1,808.64 cm 2
Circle the letter of the correct answer.
4. Which ring encloses an area of
4069.44 cm2 ?
A
Ring 2
B Ring 3
C Ring 6
D Ring 8
6. What is the area enclosed by
Ring 6?
A 5,024 cm2 B 1,600 cm2 1,256 cm2 D 62.8 cm2 C
A 3.14 square units
Copyright © by Holt, Rinehart and Winston. 42 Holt Mathematics
All rights reserved.
1
5
Official Archery
Target Ring
Diameters
Scoring Diameter
Ring (cm)
1 80
2 72
3 64
4 56
5 48
6 40
7 32
8 24
9 16
10 8
Inner 10 4
5. How much greater is the area
enclosed by Ring 10 than the area
enclosed by Ring 9?
F 50.24 cm2 150.72 cm2 H 200.96 cm2 J 251.2 cm2 G
7. What is the area enclosed by
Ring 1?
F 10 times the area of Ring 10
G 20 times the area of Ring 10
H 100 times the area of Ring 10
J 1,000 times the area of Ring 10